JP4421314B2 - Determination of slag amount in hot metal refining - Google Patents

Description

The present invention relates to a method for determining the amount of slag in the refining of hot metal in which hot metal and solid iron source are charged into a refining vessel such as converter refining, and flux is added and oxygen is blown, and in particular, de-P is performed. The present invention relates to a method for determining the amount of slag in hot metal refining , in which slag is once discharged and de-C refining is subsequently performed.

  Conventionally, as a method for producing molten steel by refining hot metal produced in a blast furnace, a process combining hot metal pretreatment and converter refining has been generally employed. Such a process mainly performs de-P or desulfurization in the preceding hot metal pretreatment, and mainly performs de-C and heat-up in the subsequent converter refining. In particular, in the converter, the de-P function of hot metal is strengthened. It has been put to practical use in order to reduce the refining load, and places importance on the functional division type refining method (so-called divided refining method).

  However, since this split refining method must have an independent pretreatment process, the cost of dedicated equipment, personnel, and materials increases, and the overall refining time becomes longer, and the heat loss is also large, so the molten steel There are not a few problems with the cost and productivity of the entire process, such as low productivity.

  The so-called double slag method (or intermediate slag method) has been developed to produce the desired molten steel only by refining by a converter without having the hot metal pretreatment facility as an effective process to solve such problems in the division refining method. Has been. The outline of this refining process is, as its name suggests, hot metal and scrap are charged into the converter and subjected to de-P treatment by adding flux and blowing oxygen to a predetermined P content (P, S content). After the reduction, the generated slag is discharged, that is, the intermediate evacuated, the furnace body is set upright, and then the de-C treatment is performed, and the steel is discharged while leaving the generated slag. This is a method (Patent Document 1, Patent Document 2, Patent Document 3, etc.) in which hot metal and scrap of the next charge are charged and flux is added and oxygen is blown in the same manner. .

  According to this method, it is possible to reduce the cost of various materials such as equipment costs, labor costs and flux for the hot metal pretreatment, reduce the refining time, and further reduce the heat loss. The

  By the way, in the de-P treatment in the double slag method, according to experiments by the inventors, predetermined conditions (total input oxygen amount (excluding de-Si)) ≧ 9 Nm 3 / molten metal t, and In the range satisfying basicity = 1.0 to 3.0), although it slightly changes depending on the operating conditions, it is generally found that the oxygen supply rate is limited in the region of [P] = 0.030% or more. It was. Furthermore, in order to reduce [P] to 0.030% or less, the P supply in the hot metal becomes the rate-determining and the efficiency is lowered. Therefore, in the first half of the de-P process, the de-P process is temporarily stopped until [P] = 0.030%, which is the oxygen supply rate-determining region, aiming at a low C / S and high-speed de-P process. It is extremely advantageous to improve the overall operation efficiency by carrying out the de-C treatment including finishing de-P after that.

In such a mode of operation, the “P distribution ratio” considered in the calculation of the auxiliary material input in the normal de-P treatment is unnecessary, and the (P ₂ O ₅ ) in the slag is the target value (based on the P material balance). = Equilibrium value) It is important to determine the minimum amount of slag (minimum slag amount) sufficient to be diluted below. In actual de-P treatment, if the operation is carried out while maintaining the de-P slag amount range with this minimum slag amount as the lower limit and slightly larger than this minimum slag amount as the upper limit, efficient de-P At the same time that P can be implemented, the total slag generation amount, that is, the total slag generation amount (the amount of slag discharged after de-P + the amount of slag generated after de-C) and the amount of slag discharged outside the system (the amount of slag discharged after P-depletion + post-C The amount of slag generated—the amount of remaining pre-charge slag) can be minimized.

However, none of the prior arts related to the above-mentioned intermediate waste disposal method pay attention to and disclose the specific operation mode of such intermediate waste disposal method, and there is no way of minimizing the amount of de-P slag. As a whole, it was not an efficient and sufficient refining method.
Japanese Patent Laid-Open No. 4-72007 Japanese Patent Laid-Open No. 5-140627 JP-A-5-247511

In view of the conventional background and circumstances, the present invention achieves target de-P effectively and reliably, and suppresses the total amount of slag generation after refining as much as possible, and produces molten steel with high efficiency as a whole. An object of the present invention is to provide a method for determining the amount of slag in the refining of possible hot metal.

According to claim 1 of the present invention, the hot metal and the solid iron source are charged into the smelting vessel, and after the de-P treatment is performed to reduce the P content by adding flux and blowing oxygen, The slag was discharged and subsequently de-C treatment was performed, and during the de-P treatment, the total oxygen supply amount excluding oxygen necessary for desiliconization was set to 9 Nm ³ / molten iron or more and slag basicity (
This is a method for determining the amount of slag in the refining of hot metal in which CaO / SiO ₂ ) is in the range of 1.0 to 3.0, and the amount of slag during the de-P treatment is determined using Equations 1 and 2. We propose a method for determining the amount of slag in hot metal refining.

P-free slag amount = M (kg / molten metal t) to M + 10 (kg / molten metal t) Formula 1
M = (input P-melting iron P after de-P treatment) × 2.29
÷ Target (P ₂ O ₅ ) concentration in slag after de-P: Formula 2
( However, the target (P ₂ O ₅ ) concentration in the slag after de-P targeted by Formula 2 is 3 to 5% by mass)
Claim 2 of the present invention considers the amount of slag adhering to the added metal and the P in the slag in calculating the de-P slag amount of Equation 1 and the input P of Equation 2. The method for determining the amount of slag in the refining of hot metal according to claim 1 is characterized.

According to a third aspect of the present invention, the slag in the refining of hot metal according to claim 1 or 2 is characterized in that the slag of the previous charge is used while remaining, and the amount of the slag remaining is adjusted using the formula 1. A method for determining the quantity is proposed.

  According to the present invention, in the hot metal refining based on the double slag method (intermediate slag method), it is possible to effectively and reliably carry out the de-P treatment targeted for the hot metal, and the total amount of slag generated and the system The amount of slag discharged to the outside can be suppressed to the minimum, which makes it possible to reduce the use of iron making agents, especially expensive basic iron making agents, and therefore to produce molten steel with high efficiency. Can be performed.

  First, in the present invention, in the de-P treatment in the first half of de-P and de-C refining, the slag is sufficiently de-P-capable, that is, the total input oxygen amount (excluding de-Si) ≧ 9 Nm 3 / molten iron t and the base Under the condition of degree = 1.0 to 3.0, high-speed de-P is performed to reduce [P] to about 0.030% (0.025 to 0.035%). After that, refining is interrupted, and the generated de-P slag is discharged while the molten iron remains in the furnace. Then, de-C treatment is performed to de-C and finish de-P (target [P] less than 0.030%). .

Since the operation mode in this de-P treatment is oxygen supply-controlled, (P ₂ O ₅ ) in the slag after de-P is less than the target value based on the mass balance of P without considering P distribution. Calculate and determine the minimum amount of slag to be diluted, that is, the minimum slag amount, and maintain the range of de-P slag amount with the minimum slag amount as the lower limit and the slag amount slightly higher than the minimum slag amount as the upper limit. To operate.

  Specifically, when the minimum slag amount is M, the de-P slag amount is determined by the following equations 1 and 2.

P-free slag amount = M (kg / molten metal t) to M + 10 (kg / molten metal t)
... Formula 1
M = (input P-melting iron P after de-P treatment) × 2.29 ÷
Target (P ₂ O ₅ ) concentration in slag after de-P: Formula 2
Even if more slag than M is used, the post-treatment hot metal [P] is not further lowered, and the amount of slag is increased only by reducing the amount of slag (P2O5). On the other hand, when less slag than M is used, sufficient de-P cannot be performed by the de-P process, and the amount of slag generated in the latter de-C process increases. Since the basicity of de-P blowing is about 1.0-2.0, the basicity of de-C blowing is high basicity operation of about 3.5-4.0, so the same amount of P is removed. In order to do this, about twice as much slag is required. Therefore, unless the operation is performed while maintaining the de-P slag amount at a value close to M, efficient de-P to achieve the target [P] will be difficult anyway, and the total slag generation amount will be reduced. Increased disadvantages.

  In the present invention, when actual operation is considered, it will be clarified by an example described later. The amount of P slag is expressed by Equation 1, and M (kg / molten metal t) is set as a lower limit to 10 (kg / molten metal t). If the upper limit is the value added, it is possible to realistically control the slag amount within this range, thereby reliably achieving the above-mentioned P removal target and effectively reducing the slag generation amount. it can.

Next, a specific calculation method when determining the amount of de-P slag by Equations 1 and 2 will be described.
1) Input P = amount of hot metal x hot metal [P] + amount of hot metal x cold iron [P] + amount of scrap x scrap [P] + amount of slag adhering to slag x amount of adhering slag (P) + amount of precharge slag x precharge Slag (P) + hot metal pan residual slag amount x pan residual slag (P)
... Formula 3
The input P is P that enters the hot metal, and is calculated according to the above formula in principle. However, if there is P mixed from other auxiliary materials other than the above, it may be calculated including this. .

  Here, the amount of scrap refers to the amount of iron scrap containing iron in the metal. In addition, the amount of slag adhering to the metal bar refers to the amount of slag that is attached to the furnace mouth of the converter or remains in the ladle after the continuous casting. This refers to the amount of slag that is charged at the same time when the slag remaining after removing the slag on the hot metal is charged into the converter. The previous charge slag amount remains after the previous charge refining (de-C treatment) and indicates the amount of slag that is used as the de-P slag for the current charge. Conventionally, in the calculation of the input P, the metal adhesion slag has not been taken into consideration.

The P concentration of slag, scrap, etc. can be calculated more accurately by measuring each charge, but a sufficient effect can be obtained by using a representative value measured separately.
2) P in hot metal after de-P treatment = amount of hot metal after de-P treatment x target after de-P treatment [P]
... Formula 4
Here, since the target P after de-P treatment changes in the oxygen supply rate-limiting region depending on the operating conditions, this value also changes from 0.025 to 0.035%, but normally a fixed value of 0.030% is used.
3) De-P slag amount = Σ (each auxiliary material, slag or main material) × [(% CaO + (% SiO ₂ )] ÷ 55% Formula 5
Here, (SiO ₂ ) is calculated as in the following equation.

(SiO ₂ ) = Amount of hot metal × Hot metal [Si] × 2.14 + Amount of cold metal × Cold iron [Si] × 2.14 + Amount of scrap × Scrap [Si] × 2.14 + Amount of slag adhering to metal + Amount of precharge slag X (SiO ₂ ) + hot metal ladle residual slag amount x (SiO ₂ ) + iron making material input x (SiO ₂ ) Formula 5-2
It should be noted that the representative value can be used for the measurement of the SiO ₂ concentration as in the case of the P concentration.

  In the calculation of the amount of de-P slag, the amount of slag adhering to the metal has not been considered at all in the past, and this has been a cause of de-P failure and the generation of wasteful slag. In particular, the slag adhering to the metal bar of the molten steel pan is composed of continuous cast slag or ingot slag, and its basicity is 2.5 to 3.5, and the slag basicity (1. Therefore, if the amount of slag is determined without taking this into consideration, it will lead to a loss of P due to poor hatching and an increase in the amount of slag generated due to excessive use of quicklime. In the present invention, by strictly adding the amount of slag adhering to the base metal to the calculation of the de-P slag amount, it is possible to further improve the accuracy of de-P and at the same time minimize the generation amount of slag.

Further, here, the amount of slag adhering to the metal is desirably determined in consideration of the amount dissolved by the de-P treatment. Since the de-P treatment in the double slag method (intermediate evacuation method) is a low temperature in a short time, the slag that is difficult to dissolve is not completely dissolved during this treatment period, and some remains undissolved There is. In such a case, the amount of adhesion slag is estimated in advance by taking into account the size and shape of the metal adhesion slag to be used and the state of charging, and a value obtained by multiplying the dissolution rate by the total amount is ground. Used as gold adhesion slag amount. The dissolution rate may be estimated based on past charge dissolution results.
3) Target post-P removal slag (P ₂ O ₅ ) concentration = 3-5% Formula 6
The slag amount after target de-P (P ₂ O ₅ ) concentration is set to 3 to 5% in the present invention from the viewpoint of making the value close to the equilibrium value. That is, if this value is less than 3%, de-P at a high speed becomes insufficient, while actual converter de-P does not easily reach a level exceeding 5%.

  As described above, the value of M (minimum slag amount) in Equation 2 is obtained, the range of the de-P slag amount in Equation 1 is determined from this value, and the de-P process is performed while maintaining the slag amount in this range. The object of the invention can be achieved.

Then, the fluctuation element of Expression 5 may be adjusted so that the amount of de-P slag satisfies the range of Expression 1. In particular, the amount of anti-fouling agent should be as small as possible in consideration of cost. Therefore, the amount of precharge slag and the amount of slag adhering to the metal is adjusted as a variable factor with a relatively large adjustment allowance. It is advantageous to use them. That is, the amount of pre-charge slag is large, and the amount of residual slag can be easily adjusted by adjusting the amount of waste discharged during steelmaking. However, when the amount of the precharge slag increases, the (P ₂ O ₅ ) concentration in the slag after de-P is reduced, resulting in an increase in slag discharge. Adjustment should be made so that the optimum amount satisfying the expression 1 is satisfied even if it is 1 or more of M.

In the treatment for hot metal containing high Si, since the basicity is lowered, the basicity during the de-P treatment is set to avoid the occurrence of the de-P slag amount greatly exceeding the value of M (minimum slag amount). It is preferable to operate by adjusting to about 1 of the minimum.
[Example]
(1) Examples 1 to 7 in the case of minimum slag amount = 50 kg / molten iron t
First, as shown in Table 1, the product standard of P of the target steel type in this example, that is, the P concentration in the molten steel after the final de-C treatment, is such that the upper limit is 0.025% and the target is 0.020%. Selected.

  Molten iron (500 Kg) was melted with a 500 Kg high-frequency furnace to adjust the hot metal, and this was charged into the hot metal pan (partially, additional reagents were added to adjust the ingredients). The adjusted hot metal components are shown in Table 2.

  Therefore, the target P of hot metal after P removal treatment is set to 0.030%, and P after the same treatment is obtained from the above equation 4. On the other hand, the pre-charge amount such as pre-charge slag and metal adhesion slag used in this treatment, etc. From the above equation, the input P in equation 3 is calculated, and the target slag (P2O5) concentration after target de-P is set to 4% to obtain the minimum slag amount obtained from equation 2, that is, M, and the range of the de-P slag amount is determined from equation 1. did. At this time, M was 50 kg / molten metal t, and therefore the range of the amount of de-slagging P was 50-60 kg / molten metal t. And based on the above-mentioned formula 5 from the range of the de-P slag amount, the usage amount of expensive basic faux-making agents such as quick lime, light doro (lightly burned dolomite), and raw doro (raw dolomite) is minimized. Recalculation was performed as much as possible, and the remaining amount of the previous charge slag was mainly adjusted. The handling of the amount of slag adhered to the metal was calculated by determining the hatching coefficient (ai) from the dissolution rate based on past experience. Here, the composition of the slag adhering to the pre-charge slag and various bullion used is shown in Table 3.

Based on the precharge slag, slag adhering slag, and slagging agent determined by such static calculation, the hot metal is put into a 500 kg top bottom blowing test converter in which scrap and bullion are placed, and quick lime is added. The de-P treatment (blowing) was performed for 5 minutes while adding the iron making agent and iron ore. Note that all oxygen was blown up, and at the same time, N ₂ gas was blown at the bottom for stirring. Tables 4 and 5 show various conditions in each example, components after treatment, temperature, and the like.

  In addition, Tables 6 and 7 show the input P, Table 8 and Table 9 show the output P and the minimum slag amount, and Tables 10 and 11 show the composition of the de-P slag and the de-P slag amount, respectively.

Next, after completion of the de-P treatment, the converter was tilted to the front side of the furnace without discharging hot metal, and the de-P slag was discharged. After that, the converter was set upright, and further demineralization treatment (blowing) was performed for 11 minutes by blowing up gaseous oxygen while adding slagging material (quick lime, light mushroom, mushroom, silica) and iron ore. went. N ₂ gas was used as the bottom blowing gas in the same manner as the de-P treatment. At the end of blowing, dynamic control was performed to adjust the target temperature to [C]. Tables 12, 13, and 14 show the various conditions and components of the de-C treatment, the blowing temperature, the de-C slag composition, and the de-C slag amount.

  Furthermore, the total slag generation amount, that is, the total slag generation amount (de-P slag discharge amount + de-C slag generation amount) and the slag discharge amount outside the system (de-P slag discharge amount + de-C slag generation) Table 15 and Table 16 show the investigation results of the amount-precharge slag remaining amount) and the investigation results on whether or not the manufactured molten steel is deviated from the P standard upper limit.

  In addition, for comparison, the same hot metal as in this example was used in the same test converter, and the operating conditions were determined by ordinary static calculation without considering the minimum slag amount during de-P treatment as in the present invention. Comparative Examples 1-1 to 1-3 and Comparative Tables 1-1 to 1-3 show the conditions of each treatment and the results after the treatment when the de-P treatment and the de-C treatment are performed in the same treatment time by the double slag method. It was written together as Examples 2-1 to 2-3. Here, as can be seen from the value of the de-P slag amount in Table 11, the group (1 to 3) of Comparative Example 1 is an example that is less than the de-P slag amount (50 to 60 Kg / molten iron t) defined in the present invention. The group (1-3) of the comparative example 2 is an example exceeding this.

  From Tables 15 and 16, it can be seen that the total slag generation amount and the slag discharge amount outside the system are considerably reduced in this example compared to the comparative example. On the other hand, P in the molten steel after de-C treatment satisfies the upper limit of the standard in this example, but some of the comparative examples (Comparative Example 1-1) are out of the upper limit. is doing. Moreover, it is also known from Table 4 that the amount of the use of a fossilizing agent such as quicklime in the de-P treatment according to this example is smaller than that of the comparative example.

  Further, the present inventors added an experiment for another comparative example for the case of this minimum slag amount = 50 kg / molten iron t, and the relationship between the de-P slag amount and the total slag discharge amount in the de-P process including these cases. Arranged. The result is shown in FIG. Furthermore, the relationship between the comparative examples 1 and 2 including the result of the additional experiment and the P standard upper limit off-rate of this example is shown in FIG.

  From FIG. 1, it is easily found that the total slag discharge amount can be minimized in the case of the present invention in which the de-P treatment is performed while maintaining the de-P slag amount in the range of 50 to 60 kg / molten iron t. In addition, it can be seen from FIG. 2 that in Comparative Example 1 carried out at a de-P slag amount of less than 50 kg / molten iron, a significant percentage of the material deviates from the upper limit of the P standard.

  From both figures, we will know the excellent effect of the present invention that performs the de-P operation while maintaining the range of the de-P slag amount with the minimum slag amount as the lower limit and the slag amount slightly larger than the minimum slag amount as the upper limit. Can do it.

The examples so far are the cases where the minimum slag amount is 50 kg / molten metal t, but the examples of the cases where the minimum slag amounts are 60 kg / molten iron t and 40 kg / molten metal t are further given the effects of the present invention. Clearly verify.
(2) Examples 1-2 in the case of minimum slag amount = 60 kg / t
In the same manner as in the above example, the de-P treatment and the de-C treatment were carried out by the double slag method when M was 60 kg / molten iron t, and therefore the range of de-P slag amount was 60 to 70 kg / mol t. Various conditions and processing results at this time are shown in Tables 17-24. Further, Comparative Examples 1-1 to 1-2 and Comparative Examples 2-1 to 2-2, which did not consider the amount of minimum slag during the P removal treatment, are also shown in the tables. Here, as can be seen from the value of the de-P slag amount in Table 22, the group (1-2) of Comparative Example 1 is an example that is less than the de-P slag amount (50-60 kg / molten iron t) specified in the present invention. The group (1-2) of Comparative Example 2 is an example exceeding this.
(3) Examples 1 and 2 in the case of minimum slag amount = 40 kg / t
The de-P treatment and de-C treatment were carried out by the double slag method when M was 40 kg / molten iron t and thus the range of de-P slag amount was 40-50 kg / mol t. Conditions and processing results at this time are shown in Tables 26 to 33. Further, Comparative Examples 1-1 to 1-2 and Comparative Examples 2-1 to 2-2, which did not consider the amount of minimum slag during the P removal treatment, are also shown in the tables. Here, as can be seen from the value of the de-P slag amount in Table 31, the group (1-2) of Comparative Example 1 is an example that is less than the de-P slag amount (40-50 kg / molten iron t) defined in the present invention. The group (1-2) of Comparative Example 2 is an example exceeding this.

  From Table 25 and Table 33 showing the results of the above-described examples of (2) and (3) and the comparative example, 50 kg of (1) even when the minimum slag amount is 60 kg / mol t and 40 kg / mol t. As in the case of hot metal t, in the case of the present invention, the total slag generation amount and slag discharge amount can be reduced as compared with the comparative example, and the result that the upper limit value of the P standard in the molten steel is sufficiently satisfied You can see that it is obtained.

FIG. 1 is a graph illustrating the relationship between the de-P slag amount and the total slag discharge amount in the de-P process when the minimum slag amount is 50 kg / molten iron t, and the results of the examples and comparative examples of the present invention. FIG. 2 is a graph illustrating the P standard upper limit deviation rate regarding the results of the examples of the present invention and the comparative example in the de-P treatment when the minimum slag amount is 50 kg / molten iron t.

Claims (3)

The hot metal and the solid iron source are charged into the smelting vessel, and flux is added and oxygen is blown into the smelting vessel to reduce the P content to a predetermined level. After that, the generated slag is discharged and continuously removed. When the C treatment is performed and the de-P treatment is performed, the total supply oxygen amount excluding oxygen necessary for desiliconization is set to 9 Nm ³ / molten iron or more and the slag basicity (CaO / SiO ₂ ) is 1.0. A method for determining the amount of slag in the refining of hot metal performed in the range of ~ 3.0,
A method for determining the amount of slag in the refining of hot metal, wherein the amount of slag in the de-P treatment is determined using Equations 1 and 2.

P-free slag amount = M (kg / molten metal t) to M + 10 (kg / molten metal t) Formula 1
M = (input P-melting iron P after de-P treatment) × 2.29
÷ Target (P ₂ O ₅ ) concentration in slag after de-P: Formula 2
(However, the target (P ₂ O ₅ ) concentration in the slag after de-P targeted by Formula 2 is 3 to 5% by mass)   2. The calculation of the de-P slag amount of Equation 1 and the input P of Equation 2 also takes into account the amount of slag adhering to the added metal and P in the slag. To determine the amount of slag in the refining of hot metal. The method for determining the amount of slag in the refining of hot metal according to claim 1 or 2, wherein the slag of the previous charge is used while remaining, and the amount of the remaining slag is adjusted using the formula 1.

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