JP4790489B2 - Converter steelmaking - Google Patents

Description

  The present invention relates to a converter steelmaking method for reusing (recycling) hot slag after de-C refining.

  Hot metal refining in conventional converters is generally performed by charging blast furnace hot metal into the converter, charging flux mainly composed of quick lime, removing P and C from hot metal by oxygen blowing, and melting steel. It was the target. After that, refining functions over multiple processes are concentrated in the converter, effectively using the energy of the hot metal, greatly reducing energy loss, and increasing fixed costs (equipment costs, labor costs) before and after the converter. There is an invention that makes it possible to reduce it easily (for example, see Patent Document 1).

  The present invention inserts hot metal into the converter as the first step, performs flux addition and oxygen blowing as the second step, performs de-Si / de-P refining, reduces to a predetermined P content, and as the third step The converter is tilted to discharge the slag generated in the second step, and then, as the fourth step, degassing is performed to the predetermined C content by flux addition and oxygen blowing in the same converter, and the fifth step. The slag produced in the fourth step is left as it is in the converter and then returned to the first step, and the process is repeated until the fifth step. In some cases, the slag was produced in the fourth step. This is a method of discharging the entire amount of slag after steel is produced in the fifth step without returning the slag to the first step.

  In addition, the process of receiving the slag generated by the pre-charge using the top-bottom blowing converter type refining apparatus without discharging (process 1), the dephosphorization refining process of hot metal (process 2), and the waste process (process 3) ), In the converter steelmaking method in which the de-C process (process 4) and the steel output process (process 5) are carried out continuously, after the process 5, the furnace is made upright with the slag remaining in the furnace. 4 or after blowing a gas mixed with one or more of nitrogen, argon, carbon monoxide and carbon dioxide from the other top blowing lance, and then perform step 1 to recycle C There is a converter steelmaking method (see, for example, Patent Document 2).

  On the other hand, a dephosphorization agent containing continuous cast iron and / or ingot-making iron and iron oxide and, if necessary, a converter iron is added to the hot metal to produce hot metal having a required oxidizing power, A hot metal dephosphorization method characterized by stirring the hot metal and the hot metal is proposed (see, for example, Patent Document 3), and at least after the de-P treatment of the hot metal is refined in a converter-type decarburization furnace. When casting through the ladle, the converter slag and / or ladle slag is recycled as part of the refining slag, or the hot metal is at least de-P treated using a converter-type pretreatment furnace and then converted. In refining in a furnace-type decarburization furnace, and then performing casting through a ladle, a method of recycling the ladle slag as a part of the pretreatment slag for P removal has been proposed (for example, Patent Document 4). reference).

Japanese Patent Laid-Open No. 4-72007 JP-A-8-199218 JP-A-5-25527 JP-A-8-53705

  In the method according to the above-mentioned patent document 1, since the de-P and de-C processes are continuously performed using the same converter, the energy of the hot metal is effectively used, and the energy loss is greatly reduced. Significant reductions in fixed costs (equipment costs, labor costs) for pre- and post-processes are possible. However, if the amount of slag discharged in the third step is small, the P removed in the slag in the second step returns to the molten steel again in the fourth step, so it is necessary to remove P again in the fourth step. In addition, the amount of flux of quicklime must be increased, which leads to an increase in cost. Moreover, since the slag having a high P concentration in the fourth step is used again in the second step, the de-P load in the second step increases, leading to an increase in cost. Thus, when there is little slag discharge | emission amount in a 3rd process, the increase in the load for performing P removal cannot be avoided, but there existed a problem of leading to a cost increase.

  Furthermore, in the method disclosed in Patent Document 1, no heat loss occurs due to the transfer of the hot metal, but the de-C slag is the T.V. Since Fe is high, there is a problem that when a molten iron of the next charge is charged in a molten state, it reacts rapidly with C in the molten iron, and so-called bumping occurs in which slag is ejected outside the furnace. In order to avoid this, lime and scrap are added to the slag as cold material before the hot metal is charged, and the converter is tilted several times, but the added coolant is cooled in the slag. Since a long time is required, there is a problem that productivity is significantly inhibited.

  When the coolant containing the CaO component is used, a part of the CaO component in the coolant remains undehumidified in the de-P slag, which hinders the use of the slag for roadbed materials and the like. Therefore, in order to use the slag, it is necessary to provide a processing time (aging period) for applying the slag to the roadbed material, which requires a period of time, and thus costs such as equipment, labor, time, etc. There was a drawback that led to up. In addition, when a scrap having a relatively large shape (100 mm or more) is used as a coolant, a long time (5 minutes or more) is required for heat transfer from the slag to the coolant. there were.

  In Patent Document 2, slag is cooled to prevent bumping at the time of hot metal charging, but argon, carbon monoxide, and carbon dioxide are used as cooling gas in a state where the converter is upright. The slag becomes supercooled, and it takes time for the slag to melt at the next de-P treatment, which leads to the extension of the treatment time and the de-P reaction efficiency.

  On the other hand, in Patent Document 3, continuous casting iron and / or ingot-making iron and, if necessary, a de-P agent containing a converter iron is added to the hot metal, but these slags have a melting point as high as 1500 ° C. or higher. Since it has a dense structure, there is a problem that melting is incomplete at the furnace temperature during the de-P treatment. When the dissolution is incomplete, the slag not only functions as a P-removing agent, but also increases the variation in P-removal and causes heat loss, leading to a significant deterioration in cost.

  Furthermore, in Patent Document 4, ladle slag is recycled, but in ladle slag, aluminum or silicon used as a deoxidizer during the generation treatment reacts with oxygen in molten steel or slag to react with alumina or Silica is produced. For example, in alumina, ladle slag contains 10 to 20% of the ladle. Therefore, the viscosity of dephosphorized soot is increased by recycle use during de-P treatment, and slopping is induced to induce the furnace. It causes a decrease in yield due to overflowing hot metal to the outside. Also, when recycling converter slag, the hot metal of the next charge is charged with a part of the converter slag of the previous charge left in the converter, and the supplementary flux material is added and recycled. The amount of slag used is preferably about 50 to 60% or less as a percentage of the total slag raw material. However, there is no method for controlling the amount of slag that remains in the converter, and slag recycling is required when actually used. There has been a problem that the accuracy of the refining itself deteriorates due to variations in the amount of slag recycled by use.

  In the above-mentioned conventional knowledge, many technical disclosures have been made regarding a method of recycling the slag of the previous charge to the next charge and recycle while still hot. However, these technologies are roughly classified into two types. The first is based on the premise that the amount of generated slag of the precharge is fully recycled, and the second is based on the assumption that a part is recycled.

  However, in the first total amount recycling premise, in continuous recycling use, the amount of slag in the furnace increases to the point where it cannot be discharged, and in addition, the phosphorus component gradually accumulates due to repeated use, resulting in de-P efficiency. It will cause adverse effects and cause problems such as returning P to molten steel. On the other hand, under the second partial recycling premise, there will be no adverse effects such as recovery P on the molten steel, but there is no way to control the amount of slag that remains in the converter. There is a problem that the accuracy of the charge refining itself deteriorates due to variations in the amount of slag that is recycled.

  The present invention aims to solve such a problem, and in the steelmaking method in which preliminary treatment and decarburization are continuously performed in a converter, when partially recycling slag in the hot recycling of slag after decarburization. Provides a method to control the amount of slag, and provides a method to recycle without deteriorating the controllability of de-P refining by accurately determining the amount that is effective for recycling, or accurately grasping the amount recycled. To do.

Hot metal into the converter or molten iron and scrap or first step of charging a molten iron and scrap and pig iron as the main raw material, slag generated in the second step the second step of performing de-Si · de P, and the converter is tilted, After the de-C refining process generated in the fifth process, the fifth process of removing the produced molten steel, and the fifth process of removing the generated molten steel. Studying how to control the amount of partially slag to be recycled after decarburization in the converter steelmaking method in which the slag is left in the furnace and then returned to the first process and the first to fifth processes are repeated. When the generated slag in the furnace was discharged after the fifth step, the results of repeated experiments to measure the weight of the residual slag in the furnace after the discharge at various tilt angles resulted in the tilt angle and the residual slag amount in the furnace. That clear correlation is obtained In addition, if the same experiment is repeated for each number of converters, the amount of slag remaining in the furnace may increase even with the same tilt angle as the number of furnaces increases. The present invention was completed by finding that there is an appropriate amount of slag to be left inside.

  The gist of the present invention is as follows.

(1) produced in the first step, the second step of performing de-Si · de P, a second step by tilting the converter to insert hot metal into the converter, or molten iron and scrap, or molten iron and scrap and pig iron as main components The third step of discharging the slag, the fourth step of standing the furnace upright and supplying oxygen from the top blowing lance to de-C, the fifth step of removing the produced molten steel, the de-C generated in the fifth step In the converter steelmaking method in which the slag after refining is left in the furnace, the process returns to the first process, and the fifth process is repeated from the first process. After the fifth process, the converter is tilted into the furnace. When part of the remaining generated slag is discharged, the amount of slag that remains in the furnace is controlled based on the tilt angle of the converter at the time of discharge, and the amount of slag that remains (WRSV) is expressed by the following equation (1) Based on the amount of slag that remains , A converter steelmaking method, characterized in that the amount of flux charged in the second charge second step is calculated.
(21 × HM [Si] × Z) / (% CaO × (Z−1)) ≦ WRSV ≦ (30 × HM [Si] × Z) / (% CaO × (Z−1.4)) (1)
Here, WRSV: target slag amount (Kg / T), HM [Si]: converter charge hot metal [Si] concentration x 0.01 (%), Z: base of slag generated and recycled in the fourth step Degree (-),% CaO: CaO concentration (%) in slag generated and recycled in the fourth step
WRSV ≦ 2.29 /% P ₂ O ₅ × A × HM [P] / (100-A) (2)
WRSV: target slag amount (Kg / T),% P ₂ O ₅ : P ₂ O ₅ concentration (%) in slag generated and recycled in the fourth step , HM [P]: converter charging molten iron [P] Concentration × 0.001 (%), A: Ratio of slag amount discharged out of the furnace in the third step among the slag amount in the furnace after the second step (%)

  (2) The converter steelmaking method as described in (1) above, wherein the converter tilt angle is corrected by the number of converters when controlling the converter tilt angle during the discharge.

  (3) The converter steelmaking method as described in (1) above, wherein the flux amount of the next charge is corrected by the number of converter furnaces.

  According to the present invention, when the slag after decarburization is reused while being hot, the amount of slag to be reused can be accurately controlled, or the amount of recycled slag can be accurately estimated. The amount of flux in the de-Si de-P process at can be accurately determined to an appropriate amount. As a result, the flux amount can be reduced and the total amount of slag discharged to the outside of the system can be reduced without deteriorating the P removal efficiency or causing an operation abnormality such as slapping. Furthermore, since the estimation of the amount of slag to be recycled has relied on the experience and intuition of the operator, the accuracy was poor, and there was a high possibility that the above-described deterioration of the P-efficiency or the operation abnormality such as slopping would occur. In order to prevent this, it was forced to operate by setting an excessive amount of flux such as quick lime to increase the basicity of the de-Si de-P process, but according to the present invention, the amount of recycled slag is accurate. Since it can be controlled well or can be estimated accurately, it is not necessary to set the basicity excessively high, and the flux can be reduced. Furthermore, regarding the slag drainage in the third step, it becomes possible to prevent the poor drainage caused by the excessive basicity due to the excessive input of flux in the second step, and the de-P load in the fourth step Is reduced, and it is possible to reduce the flux for removing P used in the fourth step and to prevent quality abnormality due to insufficient removal of P.

  The present inventors include a first step of charging hot metal, or hot metal and scrap, or hot metal and scrap and pig iron as main raw materials into the converter, a removal step of removing Si and de-P, and tilting the converter. In the third step of discharging the slag generated in two steps, the fourth step of standing the furnace upright and supplying oxygen from the top blowing lance to de-C, the fifth step and the fifth step of removing the generated molten steel In the converter steelmaking method in which the generated slag after de-C refining is left in the furnace, the process returns to the first process, and the fifth process is repeated from the first process. An industrially feasible method to improve the control accuracy of the amount of slag recycled between the two processes without reducing the refining controllability of the second process and reducing the flux for de-Si / de-P in the second process Specifically, without extending the cycle time (= raw Without lowering the sex), and without installing expensive equipment and intensive studies on methods that can be easy to implement.

  Furthermore, the total amount of slag generated in the furnace after the fifth step is recycled in addition to increasing the amount of slag in the furnace until it cannot be discharged, as described above. In consideration of the fact that it is practical to perform appropriate waste treatment because the phosphorus component gradually accumulates, which adversely affects the P removal efficiency and causes problems such as returning P to the molten steel. In this process of repeating the first step to the fifth step, it is most desirable to control the amount of slag that is recycled to the next charge at the time of evacuation work to reduce the amount of slag and prevent phosphorus concentration. I found out.

  However, conventionally, when the operator performs tilting and evacuation, an appropriate amount of the slag discharged into the slag pan is observed, for example, until the slag pan is full, for example, the slag pan In the eighth minute, etc., an appropriate guideline was set and implemented, and the optimum conditions for the amount of slag that could be recycled could not be determined. This is because it is technically difficult to accurately grasp the amount of slag generated in the furnace in the first place, but it is technically necessary to control the amount of slag to be recycled to a certain amount or to grasp the amount of slag. This is because there was no eye. Therefore, even in the conventional prior art, it must be thought that by recycling as much slag as possible, it can contribute to reducing the flux of the next charge, and as a result, the amount of recycled slag is not controlled but varies. After accepting it, they had to choose a method to reduce the amount of flux of the next charge. Alternatively, even when part of the waste is discharged, the amount of residual slag in the furnace cannot be controlled, and as a result, the amount of residual slag in the furnace must be estimated based on the experience and intuition of the operator. Therefore, it has been impossible to determine the amount of slag that can be recycled so far.

  As a method of controlling the residual slag amount in the furnace to the target amount, the present inventors set the residual slag weight in the furnace after discharging at various tilt angles when discharging the generated slag in the furnace after the fifth step. As a result of repeated experiments, it was found that a clear correlation was obtained between the tilt angle and the amount of residual slag in the furnace. Therefore, if this relationship is used, the amount of slag to be recycled can be controlled to be constant. As another operation method, from the relationship between the tilt angle and the amount of residual slag in the furnace, the tilt angle for each waste is not constant, and the amount of slag is, for example, a full pot or a pot eighth Can be accurately grasped from the tilt angle at that time, and the value of this grasped residual slag amount can be used in the second charge second process. The amount of flux reduction can be calculated accurately and accurately.

  However, it has also been found that if the same experiment is repeated for each number of converters, the amount of slag remaining in the furnace may increase with the same tilt angle as the number of furnaces increases. Therefore, if the relationship between the tilt angle and the amount of residual slag in the furnace is investigated in advance for each furnace frequency or for each furnace frequency range in a certain period, the refractories in the converter furnace associated with the use of the converter (= increase in the number of furnaces) It is possible to accurately evaluate the influence on the amount of residual slag in the furnace due to the change in the furnace shape accompanying wear and tear.

  Furthermore, it has been found that there is an appropriate amount of slag that remains in the furnace. That is, if the amount of residual slag in the furnace (= recycled slag amount) is too large, the amount of slag in the furnace will increase to the point where it cannot be discharged as described above. Accumulation of phosphorus components occurs, adversely affecting the de-P efficiency, causing problems such as returning P to the molten steel, and causing quality abnormalities exceeding the upper limit of the standard phosphorus concentration. In addition, recycled slag is slag produced by decarburization blowing and is generally a high basicity slag having a basicity of 2.5 to 4.5 or more. Even if the CaO content in the slag carried over to the next charge becomes excessive, and the CaO flux is not charged in the second step of the next charge, the appropriateness determined from the de-P efficiency in the second step and the rejectability in the third step As a result, the basicity will be exceeded, and the excretion will be deteriorated. Finally, quality abnormalities such as an increase in flux accompanying the increase in the de-P load in the fourth step of the next charge or a deviation from the standard P concentration will be caused.

  On the other hand, when the amount of residual slag in the furnace is too small, the use of additional flux for adjusting basicity such as quicklime in the second step in the next charge increases, and the effect of the present invention cannot be fully enjoyed. This causes major operational problems such as slapping due to the delay of dissolution of flux introduced in the next charge or the lack of basicity.

The present inventors have determined that the target residual slag amount that satisfies both of these conditions is the hot metal component (hot metal [Si], hot metal [P]) of the next charge, the basicity of the generated slag in the fifth charge step, Using the rejection rate of the in-furnace generated slag in the three steps, it was found that the conditions satisfying both the expressions (1) and (2) shown in claim 4 are appropriate. That is, the expressions (1) and (2) are as follows.
(21 × HM [Si] × Z) / (% CaO × (Z−1)) ≦ WRSV ≦ (30 × HM [Si] × Z) / (% CaO × (Z−1.4)) (1)
WRSV: amount of slag to be left (Kg / T), HM [Si]: converter molten iron [Si] concentration x 0.01 (%), Z: base of slag generated and recycled in the fourth step Degree (-),% CaO: means the CaO concentration (%) in the slag produced and recycled in the fourth step.
WRSV ≦ 2.29 /% P ₂ O ₅ × A × HM [P] / (100-A) (2)
WRSV: slag amount to remain (Kg / T),% P ₂ O ₅ : P ₂ O ₅ concentration (%) in slag produced and recycled in the fourth step, HM [P]: Converter charge Hot metal [P] concentration x 0.001 (%), A: The ratio (%) of the amount of slag discharged out of the furnace in the third step among the amount of slag in the furnace after the end of the second step.

  The left term in equation (1) prescribes the conditions for avoiding operational abnormalities such as slopping while maximizing the effect of reducing the amount of flux used in the second step of the next charge, and the right term is the amount of recycled slag. Stipulates the maximum amount of recycled slag so as not to deteriorate the efficiency of evacuation in the third step of the next charge. In addition, in formula (2), the phosphorus component gradually accumulates due to repeated use, adversely affects the de-P efficiency, and the maximum amount of residual slag in the furnace so as not to cause problems such as returning P to the molten steel. Is stipulated.

  These forms of the formulas (1) and (2) reflect all the conditions necessary for operation in a simple structure applicable to actual operation, and the present inventors have actually calculated the respective coefficients. It is a value found so that the optimum condition is obtained by repeating many tests in the operation.

  Furthermore, although the method of the present invention for controlling the amount of recycled slag to a target amount is an extremely simple method, it has been noted that the amount of slag remaining in the furnace at the time of tilting is controlled by the furnace shape. This is a new idea that has never existed before. Therefore, according to this method, the furnace shape varies depending on the establishment and converter to be implemented, so the relationship between the tilt angle at the time of discharge and the amount of residual slag in the furnace is characteristic, while any As a very general general-purpose technology that can be applied to furnaces, it can greatly contribute to improving controllability.

  These proper T.P. Although there has been a qualitative way of thinking about CaO in the past, the amount of slag to be recycled is unknown, or due to large variations in operation based on experience and intuition, it could not be applied to actual operations so far. . Even if it is applied, as described above, quality abnormalities or operational abnormalities such as slopping frequently occur. The amount of slag recycled by the method of the present invention can be controlled quantitatively, with high accuracy, with good reproducibility, and easily, and the amount of slag remaining in the furnace can be estimated quantitatively with high accuracy from the actual tilt angle. Appropriate T.O. The amount of CaO was found.

  The details will be described below based on application examples in a converter.

  FIG. 1 shows a schematic view of exhausting by tilting the converter. Conventionally, the waste was removed in the fifth step in the form shown in FIG. That is, the operator tilts the converter 1 and performs the tilting operation of the converter 1 while watching the amount of discharged slag 3 discharged from the converter 1 into the waste pan 2 mounted on the slag transport facility 8. The end timing of exclusion was determined. Therefore, the amount of residual slag 4 in the furnace remaining in the furnace was estimated based on experience and intuition from the amount of slag discharged into the slag pan 2, and the amount of flux in the next charge second step was determined. is there.

  In the method of the present invention, based on a new idea, the relationship between the tilt angle (α) 5 formed by the horizontal line 6 and the converter center horizontal line 7 at the time of discharge and the amount of residual slag 4 remaining in the furnace. The amount of slag recycled to the next charge was always made constant by setting the operation to a constant operation at an appropriate tilt angle α.

  Specifically, FIG. 2 shows the relationship between the furnace tilt angle and the amount of residual slag in the furnace when the number of furnaces is 1000 to 1500. For example, in a certain converter, the tilt angle α is 70 ° to the outside of the furnace. The amount of slag discharged to the outside of the furnace increases as the tilting angle increases and then the tilt angle increases, that is, the amount of slag remaining in the furnace decreases, and the slag that remains in the furnace at a tilt angle of 120 ° The amount is zero. That is, the entire amount is rejected. It was confirmed that this can be realized with extremely good reproducibility if the number of furnaces is almost the same. In addition, since this tilt angle changes with converter vessel shapes, it is necessary to determine the relationship between the tilt angle and the amount of residual slag in a furnace according to the converter vessel shape for every establishment which implements this invention.

  Therefore, in the converter, the tilt angle α is controlled to 90 ° to 110 °, and the amount of slag to be hot recycled to the residual / next charge in the furnace is controlled to 20 to 40 kg / T.

  The appropriate value of the tilt angle α has an appropriate flux amount in consideration of the refining conditions in the next charge, for example, the silicon concentration in the hot metal, the blowing temperature in the fourth process, the upper limit of the standard phosphorus concentration in the product, etc. The amount of residual recycled slag is controlled appropriately according to the respective refining conditions. In addition, even when the tilt angle α deviates from the planned α, the amount of slag remaining in the furnace can be accurately estimated by using the relationship shown in FIG. If it is reflected in, optimum conditions can always be reproduced without adversely affecting the operation.

  In addition, the converter is lined with refractory inside, and every time the refining process is performed, the shape inside the furnace changes with time, although it is slightly melted. Therefore, the relationship between the tilt angle α and the amount of residual slag in the furnace changes as the number of furnaces increases. The present inventors paid attention to this and determined the relationship between the number of furnaces and the amount of residual slag in the furnace by actually weighing each tilt angle α. FIG. 3 shows an example of the relationship between the number of furnaces and the amount of residual slag in the furnace when the tilt angle α is 105 ° in the converter. As shown in FIG. 3, even if the tilt angle α is a constant value of 105 °, the residual slag amount increases as the number of converters increases. If the tilt angle α is corrected to an angle larger than 105 °, a target residual slag amount can be obtained. The present inventors refer to the table based on the relationship of FIG. 3 for each number of converters during refining this time, and always achieve the target accurately with the recycle slag amount control technology based on the tilt angle control described above. The amount of residual slag is realized.

  Further, the amount of flux of the next charge can be corrected according to the number of converters. Specifically, depending on the number of converters, the amount of residual slag increases as shown in FIG. 3. For example, in the case of 1000 to 1500 converters, the slag amount per unit is about 25 kg / T. When the number of furnaces is 1500 to 2000, the basic unit of slag amount increases by about 10%. By reducing the flux amount of the next charge according to the increased amount, the converter tilt angle α is not changed. You can carry out dredging.

  The relationships illustrated in FIG. 2 and FIG. 3 clearly show characteristic relationships depending on the shape of the converter, and in implementing the present invention, these relationships are investigated in advance at each office. You can enjoy the effect.

  As described above, according to the present invention, it is considered that the amount of slag to be hot recycled after the fifth step can be accurately controlled or estimated accurately, and thus the effect in actual machine operation was verified.

FIG. 4 is a diagram comparing the slag basicity controllability in the second step (de-Si / de-P) by implementing the method of the present invention and the conventional method N = 1000 times using a 370 ton converter. As shown in FIG. 4, in the conventional method, the residual slag in the furnace was recycled after the fifth step. Due to the poor accuracy of estimating the amount of slag, a flux containing excessive lime was used in the second step of the next charge. In other words, in the method of the present invention, the control accuracy of the target appropriate basicity (1.1 to 1.4) is increased, and the slag of the next charge can be accurately controlled. It became possible, and it became possible to refine without adding excessive flux.
In addition, Table 1 shows an example of actual operation using a 370 ton converter. This will be described in detail below.

Here, the main numerical values used in calculating the appropriate slag amount used in the calculations of the equations (1) and (2) in the above are: (% CaO) = 50%, (% P ₂ O ₅ ) = 3%, slag discharge ratio in the third step = 40%, and target basicity X in the second step = 1.2.

  Since the amount of recycled slag was unknown in the conventional methods 1 and 2, which are conventional examples, exactly the same as before (exhaust based on the experience of the operator, visually confirming the slag situation in the exhaust pan and the furnace The value obtained by calculating the residual slag amount in the furnace from the converter tilt angle α after the operation is described as “WRSV” after the operation by the method of (estimating the inner slag amount). For reference, the residual slag amount in the furnace estimated by the worker at that time is also shown as “WRSV by worker estimation”. In the conventional method 1, the waste was discharged at the furnace tilt angle α = 99 ° during the discharge, and the worker estimated the residual slag amount in the furnace (WRSV estimated by the worker) to be about 13 kg / T. It happened based on that. Further, in the conventional method 2, waste was discharged at a furnace tilt angle α = 112 ° at the time of discharge, and the worker estimated that the amount of residual slag in the furnace (WRSV estimated by the worker) was about 31 kg / T. Based on this, slag basicity in the second step of the next charge (basicity after de-Si-de-P treatment) = 1.2 aimed at reducing the amount of quicklime (second step T.CaO) = 2.2 kg / T. Since the residual slag amount in the furnace (WRSV) was 21 kg / T, the CaO content from the recycled slag was less than expected, and as a result, the basicity of the next charge second step (basicity after de-Si de-P treatment) Can only secure up to 0.9, causing slapping.

  On the other hand, in the present method 1, which is an embodiment of the present invention method, a recycle slag amount target value is determined based on the calculation formulas (1) and (2), and the tilt angle at the time of discharge is controlled for the furnace. The amount of residual slag was controlled as planned. Actually, when the second step was processed with quick lime zero, the slag basicity after the end of the second step was 1.1 as planned, as the amount of recycled slag was accurately determined, but within the proper operating range. Control was possible, and there was no operational abnormality such as evacuation in the third step and slopping in the second step. Further, in the present method 2 of the embodiment of the present invention method, the residual slag amount in the furnace (WRSV) = 30 kg / T, which is the target amount of recycled slag, and the target tilt angle α at the time of removal for that purpose = 104 °. However, since the tilting has been completed at the actual tilting angle α = 100 °, the actual residual slag amount in the furnace (WRSV) = 35 kg / T. In the range, by keeping the amount of quick lime in the second step of the next charge appropriately, the slag basicity (basicity after de-Si de-P treatment) of the second step can be set to 1.2 as intended. As in the case of No. 1, proper processing without any operational problems was realized. Furthermore, in Method 3 of the embodiment of the method of the present invention, the residual slag amount in the furnace (WRSV) = 24 Kg / T, which is the target amount of recycled slag, and the target tilt angle α during discharge for that purpose = 105 Therefore, the removal was completed with a tilt angle of α = 105 ° as a target, and 24 kg / T of slag was left in the furnace. As a result of adding 2.5 kg / T quicklime in the second step, the basicity of the slag in the furnace after the second step treatment could be controlled within an appropriate range, and the operational problems were similar to the present methods 1 and 2. We realized proper processing that was not at all. As can be seen by comparing Method 1, Method 2, and Method 3 with Conventional Method 1 and Method 2, the basicity, which is an important operational index in the second step, varies little with the target value in this method. On the other hand, in the conventional method, the basicity in the second step as a result is greatly different from the target due to variations in the amount of recycled slag. As a result, in this method, compared with the conventional method, the P removal treatment in the second step was realized stably, and the rejection rate and operability were both stabilized very well. As a result, it was possible to reduce the de-P load in the fourth step and reduce the amount of quicklime.

  In addition, although the Example shown here is an example at the time of setting the slag discharge | emission ratio in a 3rd process = 40%, it can confirm that this value can be implemented between 20 to 80%. ing.

It is the schematic which is rejected by tilting a converter. It is a figure which shows the result of having measured the slag weight which remained in the furnace for every inclination angle (alpha). It is a figure which shows the relationship between the frequency | count of a converter furnace and the residual slag weight in a furnace at the time of tilting angle 105 degrees. It is a figure which shows the difference in the slag basicity controllability in the de-Si de-P phase by the presence or absence of implementation of this invention method.

Explanation of symbols

1 Converter 2 Waste pan 3 Waste slag 4 Remaining slag 5 Inclination angle α
6 Horizontal line 7 Converter horizontal line 8 Slag transportation equipment

Claims (3)

Hot metal in the converter, or hot metal scrap or pig iron in the first step of inserting the scrap and pig iron as main components, a second step of performing de-Si · de P, and slag produced in the second step by tilting the converter After the de-C refining process generated in the third process, the fourth process in which the furnace is kept upright and oxygen is supplied from the top blowing lance to de-C, the fifth process in which the produced molten steel is removed, and the fifth process. In the converter steelmaking method in which the slag is left in the furnace and then returned to the first step, and the fifth step is repeatedly performed from the first step, after the fifth step, the converter is tilted and remains in the furnace. When part of the generated slag is discharged, the amount of slag remaining in the furnace is controlled based on the tilt angle of the converter at the time of discharge, and the amount of remaining slag (WRSV) is expressed by the following formula (1) and (2 ) is calculated so as to satisfy both equations, following tea based on the amount of slag to remain BOF steelmaking method characterized by calculating the amount of flux to be introduced with di second step.
(21 × HM [Si] × Z) / (% CaO × (Z−1)) ≦ WRSV ≦ (30 × HM [Si] × Z) / (% CaO × (Z−1.4)) (1)
Here, WRSV: target slag amount (Kg / T), HM [Si]: converter charge hot metal [Si] concentration x 0.01 (%), Z: base of slag generated and recycled in the fourth step Degree (-),% CaO: CaO concentration (%) in slag generated and recycled in the fourth step
WRSV ≦ 2.29 /% P ₂ O ₅ × A × HM [P] / (100-A) (2)
WRSV: target slag amount (Kg / T),% P ₂ O ₅ : P ₂ O ₅ concentration (%) in slag generated and recycled in the fourth step , HM [P]: converter charging molten iron [P] Concentration × 0.001 (%), A: Ratio of slag amount discharged out of the furnace in the third step among the slag amount in the furnace after the second step (%)   2. The converter steelmaking method according to claim 1, wherein the converter tilt angle is corrected by the number of converters when the converter tilt angle at the time of discharge is controlled.   The converter steelmaking method according to claim 1, wherein the amount of flux in the second charge second step is corrected by the number of converter furnaces.

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