JP4937828B2 - Blowing method of molten steel - Google Patents

Description

  The present invention relates to a molten steel blowing method for reusing slag generated by decarburization processing in a converter.

  As a method for blowing molten steel in a converter, there is a method of increasing the purity of steel and suppressing the amount of slag discharged by reusing slag produced by decarburization for dephosphorization of the next charge. In this method of reusing decarburized slag, after the hot metal pretreatment in the converter, the slag with high phosphorus concentration is discharged once out of the converter (intermediate waste), and the desiliconized and dephosphorized hot metal is removed. Is left in the converter, new slag is added, and the remaining phosphorus is removed (finish dephosphorization) and decarburized and blown. After decarburization blowing, only molten steel is produced, and slag with low phosphorus concentration remaining in the converter is reused for hot metal pretreatment for the next charge.

  In the method of reusing decarburized slag, the amount of CaO required for final dephosphorization is added during decarburization blowing, but it is necessary during hot metal pretreatment if the Si concentration in the hot metal discharged from the blast furnace is high In order to ensure basicity, only CaO contained in the slag after decarburization is not sufficient, and it is necessary to newly add CaO to the slag.

  However, when CaO is newly added during the hot metal pretreatment, the treatment time of the hot metal pretreatment, that is, the blowing time of desiliconization and dephosphorization is short, so the CaO added to the slag is not completely dissolved, and some Of CaO remains in the slag as undehydrated CaO. Since the undehydrated CaO remaining in the slag causes a hydration reaction, there is a problem that the volume of the slag is expanded and the quality of the slag is lowered.

  In order to solve such problems, the decarburized soot from the previous converter blowing is left in the converter, and the decarburized soot is reused for the dephosphorization treatment of the next charge. A converter steelmaking method for reusing a decarburization slag (hereinafter also referred to as decarburization slag) characterized by adjusting the amount of Si in the hot metal charged into the converter according to the amount of effective CaO present has been proposed. (For example, refer to Patent Document 1). In the steelmaking method of Patent Document 1, when using decharged decarburized slag at the time of dephosphorization, a converter is previously provided so that a predetermined basicity can be obtained without newly adding massive CaO. This is a technique of desiliconizing the hot metal to be charged in the steel.

JP 2001-123214 A

  However, as in the steelmaking method of Patent Document 1, in order to desiliconize the hot metal in advance, a desiliconization treatment facility must be newly installed, which increases the cost for capital investment. there were. In addition, depending on the reaction vessel in which desiliconization is performed, it is necessary to use a solid oxygen component such as iron oxide as an oxygen source for desiliconization, and heat loss due to reduction heat such as iron oxide occurs. There was also.

  Therefore, the present invention has been made in view of such problems, and in a molten steel blowing method for reusing slag generated by decarburization processing in a converter, an increase in cost, loss of heat, and the like occur. It aims at suppressing generation | occurrence | production of the non-deoxidized CaO accompanying new CaO addition at the time of hot metal preliminary processing.

  As a result of intensive research in order to solve the above problems, the present inventors considered conditions such as the Si concentration and basicity of the molten iron in the next charge when performing decarburization blowing of a certain charge. By calculating the amount of CaO that is expected to be added in the hot metal pretreatment of the charge, and adding the determined amount of CaO to the converter in advance during the decarburization blowing of the charge, It has been found that it is not necessary to add new CaO during the hot metal pretreatment of the charge, and the generation of undehydrated CaO can be suppressed, and the present invention has been completed based on this finding.

That is, the gist of the present invention is as follows.
(1) A hot metal preliminary treatment step in which desiliconization and dephosphorization are performed by blowing hot metal in a converter charged with CaO in an amount that makes the basicity of slag the target basicity, and the hot metal preliminary treatment An intermediate waste process for discharging the slag after the treatment process from the converter, and a decarburization process process for performing decarburization and final dephosphorization by adding CaO into the converter and blowing it are repeated in order. Performing a slag after the decarburization process at the nth charge, and reusing the slag for the hot metal pretreatment process at the (n + 1) th charge, in the decarburization process at the nth charge A method for blowing molten steel, characterized in that the amount of CaO to be added is set to a CaO amount capable of ensuring the target basicity in at least the (n + 1) charge hot metal preliminary treatment step.
(2) The amount of CaO added in the decarburization process step of the n-th charge is the amount of CaO necessary for the final dephosphorization in the decarburization process step of the n-charge and the hot metal pretreatment step of the (n + 1) -th charge The method for blowing molten steel according to (1), characterized in that it is an amount satisfying any CaO amount necessary for obtaining the target basicity.
(3) The amount of slag discharged in the intermediate discharge step of the n-th charge is determined based on the addition amount of CaO necessary for the final dephosphorization in the decarburization processing step of the n-charge and the hot metal reserve of the (n + 1) -th charge The molten steel blowing method according to (1) or (2), characterized in that the addition amount of CaO necessary for obtaining the target basicity in the treatment step is equivalent.
(4) The addition amount of CaO in the decarburization process step of the n-th charge is characterized by being the CaO amount of the larger of the CaO amounts calculated by the following formula (I) or (II): The method for blowing molten steel according to any one of (1) to (3).
W _{P, CaO} = 1000 / Lp <n> × (B2 [P] i <n> / target [P] f <n> +1) × (% CaO) B2 <n> −R _{B1, CaO <n>.} .. (I)
W _{Si, CaO} = (HM [Si] <n + 1> × 60/28 × 10 + R _{SiO2 <n>} ) × (B1C / S <n + 1>) − R′CaO _<n> (II)
However, each parameter in the formulas (I) and (II) is as follows.
WP _{, CaO: The} amount of CaO necessary for dephosphorization in the fourth step of the n-th charge Lp <n>... Estimated phosphorus distribution in the fourth step of the n-th charge B2 [P] i <n> ..Phosphorus concentration carried over to the 4th step of the n-th charge (converted to phosphorus concentration in molten iron)
Target [P] f <n> ... target phosphorus concentration after the fourth charge of the n-th charge (% CaO) B2 <n> ... CaO in the slag after the fourth charge of the n-charge Estimated concentration R _{B1, CaO <n>} ... The amount of CaO carried over from the second step of the n-th charge to the fourth step through the third step W _{Si, CaO} . The amount of CaO to be added in the fourth step of the n-th charge necessary to secure the basicity target value in the step HM [Si] <n + 1> (n + 1) hot metal charged into the converter at the charge point from the density R _{SiO2 <n>} ··· _n charge th Si in, at (n + 1) SiO ₂ amount is recycled to the charge th B1C / S <n + 1> ··· (n + 1) charge th second step basicity target value R _{'CaO <n>} ··· _n or charge th , (N + 1) of the amount of CaO to be recycled to the charge eyes, CaO amount excluding the amount to be added by n charge th fourth step

  According to the present invention, in the molten steel blowing method for reusing the slag generated by the decarburization process in the converter, conditions such as the Si concentration and the basicity of the hot metal of the next charge are taken into account, and the hot metal reserve of the next charge is considered. The amount of CaO that is expected to be added in the process is determined, and the determined amount of CaO is added to the converter in advance during decarburization blowing of the previous charge, so that the hot metal for the next charge is added. Since it is not necessary to add new CaO during the preliminary treatment, it is possible to suppress the generation of undehydrated CaO. Therefore, according to the present invention, the hydration reaction of undehydrated CaO in the slag can also be suppressed, and the quality of the slag can be improved.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

  First, prior to explaining a method for blowing molten steel according to an embodiment of the present invention, an outline of a method for operating a converter by a method of reusing so-called decarburized slag as a premise thereof will be described. In addition, FIG. 1 is explanatory drawing which shows the outline | summary of the operating method of the converter by the method of reusing decarburization slag.

  As shown in FIG. 1, in the converter operating method by the method of reusing decarburized slag, when producing molten steel by blowing blast furnace hot metal subjected to desulfurization treatment, the first step described below The sixth step is repeated in order. In the following description, it is assumed that the charge of interest is the nth charge (n is a natural number), and the next charge is the (n + 1) th charge.

  In the first step (n-th charge), for example, the molten iron 110 subjected to the desulfurization treatment from the ladle 20 is charged into the converter 10 in which the iron scrap 120 is charged. As the converter 10 to be used, an upper-bottom converter is generally used.

  In the second step (n-th charge), a flux such as CaO is added into the converter 10 charged with the molten iron 110, and a low basicity (for example, basicity 2 or less) slag 130 is used at low temperature conditions ( For example, desiliconization / dephosphorization blowing (hot metal pretreatment) is performed in a short time (for example, about 3 to 8 minutes) while blowing oxygen or air from the top blowing lance 30 or the like at 1250 to 1400 ° C. (Blow 1 ). By this hot metal preliminary treatment, Si in the hot metal 110 is completely removed in the slag 130, but a part of P remains in the hot metal 110.

  In the third step (nth charge), the slag 130 generated by the hot metal preliminary treatment in the second step is discharged from the converter 10 to the discharge pan 40 or the like installed in the cart 50 (intermediate discharge). At this time, since only the slag 130 is discharged by tilting the converter 10 while the hot metal 110 remains in the converter 10, it is difficult to completely discharge the slag 130 from the converter 10. About 70 to 80% of the slag 130 in the furnace 10 can be discharged outside the furnace (hereinafter, the ratio of the amount of slag discharged at the time of intermediate discharge to the amount of slag after the hot metal pretreatment is expressed as “rejection rate (%) ”). Here, the slag 130 remaining in the converter 10 is carried over to the next fourth step.

  In the fourth step (n-th charge), flux is newly added into the converter 10, and at a predetermined temperature (for example, 1600 to 1700 ° C.) so that the C concentration in the molten steel 110 becomes a desired concentration. Decarburization blowing is performed while blowing oxygen from the top blowing lance 30 and the bottom blowing nozzle (not shown) (Blow 2). At this time, a flux such as CaO is added to the converter 10 so that the P concentration in the molten steel 110 becomes a desired concentration (for example, about 0.01 to 0.03 mass%), and finish dephosphorization (molten steel 110). (Removal of a slight amount of P remaining therein).

Here, the P content (mainly present as P ₂ O ₅ ) in the slag 130 remaining in the third step is restored to the molten steel 110 during decarburization blowing. Therefore, by reducing the amount of slag 130 remaining in the third step, that is, by increasing the amount of slag 130 discharged during intermediate evacuation, the amount of P to be recovered decreases, so the addition of a flux such as CaO The amount can be reduced. However, compared with the temperature condition in the decarburization / dephosphorization blowing in the second step, the temperature condition in the decarburization blowing in the fourth step is a high temperature condition unfavorable for dephosphorization. It is necessary to increase the basicity of the slag 130.

  In the fifth step (n-th charge), the decarburized slag 130 generated by the decarburization blowing in the fourth step is left in the converter 10, and the converter 10 is tilted to remove the molten steel 110. Do.

  In the sixth step (nth charge), after the converter 10 tilted in the fifth step is set upright, the decarburized slag 130 generated in the fourth step is solidified in the converter 10 and recycled. Note that iron scrap may be charged into the converter 10 when the slag 130 is solidified.

  After solidifying the slag 130 in this way, the process returns again to the first step ((n + 1) charge), and the hot metal 110 is charged into the converter 10 where the solidified slag 130 remains, and the nth charge The entire amount of slag 130 generated in the fourth step and solidified in the converter 10 in the sixth step is reused as a flux for desiliconization / dephosphorization in the second step of the (n + 1) charge. Since the decarburization slag in the fourth step has further dephosphorization ability under the dephosphorization blowing conditions, the amount of flux such as CaO used at the dephosphorization blowing can be reduced.

  Next, based on FIGS. 2-4, the molten steel blowing method which concerns on the 1st and 2nd embodiment of this invention is demonstrated. In addition, FIG. 2 shows an example of the relationship between the slag rejection rate (%) during the intermediate rejection in the third step and the CaO addition amount (kg / t) during the decarburization blowing (Blow 2) in the fourth step. The horizontal axis represents the slag removal rate (%), and the vertical axis represents the CaO addition amount (kg / t) during decarburization blowing. Moreover, FIG. 3 is explanatory drawing which shows the flow of the blowing method of the molten steel which concerns on the 1st Embodiment of this invention. Moreover, FIG. 4 is explanatory drawing which shows the flow of the blowing method of the molten steel which concerns on the 2nd Embodiment of this invention.

Here, the experimental conditions in FIG. 2 were performed as follows. That is, the target P concentration in the fourth step of the n-th charge is 20 × 0.001 mass%, the distribution of the blow-off P concentration in the same step is 86, the CaO concentration after the processing in the same step is 47%, (n + 1) charge The target basicity of the second step in the eye was 1.4, and the Si concentration in the hot metal was 41 × 0.01 mass%. In addition, the amount of CaO carried over from the second step and the P concentration charged in the fourth step fluctuate depending on the rejection rate, and the amount of recycled SiO ₂ was 3.7 kg / t, excluding the amount added in the fourth step. The amount of recycled CaO was 1 kg / t.

(Method for blowing molten steel according to the first embodiment)
In the method of reusing decarburized slag as described above, CaO used as a flux for desiliconization or dephosphorization is generally added to a converter as follows. That is, assuming that the slag rejection rate during the intermediate rejection in the third process of the n charge is 70%, for example, in the fourth process of the n charge as shown in the plot of [1] in FIG. Add only the amount of CaO (about 15.7 kg / t) necessary for the final dephosphorization. The slag generated in the fourth process of the n-th charge is reused as a flux for desiliconization / dephosphorization in the second process of the (n + 1) -th charge. Here, in general, only the decarburized slag generated in the fourth process of the reused n charge has the basicity required for the desiliconization / dephosphorization in the second process of the (n + 1) charge. As shown in the plot of [2] in FIG. 2, CaO is newly added so that the amount of CaO necessary for the second step of the (n + 1) charge (about 16.5 kg / t) is reached. There is a need.

  However, in such an operation, since the desiliconization / dephosphorization in the second step is performed in a short time, the newly added CaO is not completely dissolved in the slag and remains in the slag as undehydrated CaO. End up. As a result, the undehydrated CaO undergoes a hydration reaction, and the slag expands in volume, resulting in a deterioration in the quality of the slag.

  Therefore, in the molten steel blowing method according to the first embodiment of the present invention, as shown in FIG. 3, the conditions such as the Si concentration in the hot metal of the (n + 1) charge and the target basicity are taken into consideration. The amount of CaO expected to be required in the second step of the (n + 1) charge is calculated in advance, and the calculated amount of CaO is converted into the amount of CaO required in the fourth step of the n charge. Are added at the same time.

Here, a specific example of a method for calculating the CaO amount will be described. In the molten steel blowing method according to the present embodiment, for example, the addition amount of CaO in the fourth step of the n-th charge is the larger of the CaO amounts calculated by the following formula (I) or (II): It can be the amount of CaO.
W _{P, CaO} = 1000 / Lp <n> × (B2 [P] i <n> / target [P] f <n> +1) × (% CaO) B2 <n> −R _{B1, CaO <n>.} .. (I)
W _{Si, CaO} = (HM [Si] <n + 1> × 60/28 × 10 + R _{SiO2 <n>} ) × (B1C / S <n + 1>) − R′CaO _<n> (II)

Here, the meaning of each parameter in the above formulas (I) and (II) is as follows.
WP _{, CaO: The} amount of CaO necessary for dephosphorization in the fourth step of the n-th charge Lp <n>... Estimated phosphorus distribution in the fourth step of the n-th charge B2 [P] i <n> ..Phosphorus concentration carried over to the 4th step of the n-th charge (converted to phosphorus concentration in molten iron)
Target [P] f <n> ... target phosphorus concentration after the fourth charge of the n-th charge (% CaO) B2 <n> ... CaO in the slag after the fourth charge of the n-charge Estimated concentration R _{B1, CaO <n>} ... The amount of CaO carried over from the second step of the n-th charge to the fourth step through the third step W _{Si, CaO} . The amount of CaO to be added in the fourth step of the n-th charge necessary to secure the basicity target value in the step HM [Si] <n + 1> (n + 1) hot metal charged into the converter at the charge point from the density R _{SiO2 <n>} ··· _n charge th Si in, at (n + 1) SiO ₂ amount is recycled to the charge th B1C / S <n + 1> ··· (n + 1) charge th second step basicity target value R _{'CaO <n>} ··· _n or charge th , (N + 1) of the amount of CaO to be recycled to the charge eyes, CaO amount excluding the amount to be added by n charge th fourth step

  In the example of FIG. 2, since the rejection rate is 70%, the CaO amount [2] is added prior to the fourth step of the n-th charge. Thus, the total amount of CaO charged in the converter is not changed in the fourth step of the nth charge and the second step of the (n + 1) th charge, and the second step of the (n + 1) th charge is newly changed. It is possible to prevent CaO from being added. That is, in the molten steel blowing method according to the present embodiment, in the decarburization blowing in the fourth step of the nth charge, the amount of CaO contained in the slag generated by the decarburization blowing is the (n + 1) th charge. The addition amount of CaO is determined in advance so that the amount of CaO used in the hot metal preliminary treatment step in the second step can be secured, and the determined amount of CaO is added in the fourth step of the n charge. There is a big difference from the conventional method.

Next, the molten steel blowing method according to the present embodiment will be described more specifically based on FIG. First, the abbreviations used in FIG. 3 will be described before a specific description. “BI” and “BII” mean Blow 1 (desiliconization / dephosphorization blowing) and Blow 2 (decarburization blowing). “W1CaO” and “W2CaO” indicate the amount of CaO added by Blow 1 (desiliconization / dephosphorization blowing) and the amount of CaO added by Blow 2 (decarburization blowing), respectively. HM [Si] indicates the Si concentration in the hot metal, C / S indicates the basicity (CaO / SiO ₂ ), and [P] f indicates the target value of the P concentration in the molten steel at the end of blowing. <1>, <2>, etc. indicate the first charge, the second charge, and the like.

  When desiliconization / dephosphorization blowing (BI) of the first charge is started, an action of adding an amount of CaO necessary for desiliconization / dephosphorization blowing of the first charge is performed (W1CaO <1>). ). As a result of this desiliconization and dephosphorization, the actual results are obtained as clarified information, and at this point, the Si concentration (HM [Si] <2>) in the second charge blast furnace hot metal is also obtained as clarified information. Therefore, based on this information and information on the basicity of slag (BIC / S <2>) targeted for desiliconization and dephosphorization blowing at the second charge, etc. The amount of CaO to be added in the first charge decarburization blowing including the amount of CaO required in the dephosphorization blowing (next channel required W2CaO <1>) is calculated. Both of these calculations are performed before intermediate rejection.

  Next, the intermediate charge of the first charge is performed. By this intermediate rejection, information on the rejection rate (rejection rate <1>) of the first charge is found.

  Decarburization blowing (BII) is started after the end of the intermediate waste, and the amount of CaO added at this time is the next channel required W2CaO <1> calculated as described above and the end of decarburization blowing. It can be calculated from the target value of the P concentration at the time, the target value of the blow-off temperature, and the like. It can be determined by comparison with the amount of CaO necessary to ensure dephosphorization in decarburization blowing (the ch required W2CaO <1>). After the decarburization blowing (BII) is completed, the generated decarburized slag is recycled in the furnace. At that time, information on the amount of slag (recycled amount) to be reused for desiliconization / dephosphorization at the second charge and the components of the slag are found.

  Next, decarburization slag of the first charge is reused, and desiliconization / dephosphorization blowing (BI) of the second charge is started. Since the CaO necessary at this time has already been added during the decarburization blowing of the first charge, the amount of CaO (W1CaO <2>) added during the desiliconization / dephosphorization blowing of the second charge Can be zero. At this time, the results of desiliconization / dephosphorization blowing at the second charge, Si concentration (HM [Si] <3>) in the blast furnace hot metal at the third charge, and desiliconization / dephosphorization at the third charge Decarburization blowing of the second charge including the amount of CaO required for desiliconization and dephosphorization blowing of the third charge from information such as basicity of slag (BIC / S <3>) Calculating the amount of CaO to be added at (the next channel required W2CaO <2>) is the same as in the first charge. In this way, by repeating the steps from desiliconization / dephosphorization treatment to recycling, it is possible to effectively utilize slag while suppressing the generation of undehydrated CaO.

  In the molten steel blowing method according to the present embodiment, when adjusting the amount of slag discharged at the time of intermediate discharge, a weighing machine is provided on the carriage 50 on which the discharge pan 40 is loaded, and slag discharge is performed. By measuring the amount and using the actual value, it is possible to further improve the accuracy of suppressing the generation of unfogged CaO in the intermediate slag.

  Thus, unlike the conventional case, CaO added to the converter can be completely dissolved in the slag by adding CaO from the time of decarburization blowing in the fourth step, which takes a long time. In the second step of the (n + 1) th charge, the desiliconization / dephosphorization treatment can be performed using CaO completely dissolved in the slag, and the generation of undenitrated CaO can be suppressed.

(Method for blowing molten steel according to the second embodiment)
However, the operation as described above is excellent in that it is not necessary to newly add CaO in the second step of the (n + 1) th charge and the generation of undeoxidized CaO can be suppressed. The amount of CaO added in the four steps is excessively added to the dephosphorization treatment in the fourth step, and excessive dephosphorization may occur.

  Therefore, in the molten steel blowing method according to the second embodiment of the present invention, the amount of CaO required for the hot metal pretreatment (desiliconization / dephosphorization) in the second step of (n + 1) charge and the nth charge. The slag rejection rate of the intermediate rejection in the third step of the n-th charge is determined so that the amount of CaO necessary for the final dephosphorization in the fourth step becomes equal. In the example of FIG. 2, as shown in [3] of FIG. 2, the slag rejection rate of the intermediate rejection in the third step of the n-th charge is the desiliconization / dephosphorization rate in the second step of the (n + 1) -th charge. The slag rejection rate that satisfies the condition that the amount of CaO necessary for the dephosphorization and the amount of CaO necessary for dephosphorization in the fourth step of the n-th charge is 55%. Thereby, even in the fourth step of the n-th charge, the amount of CaO required for the final dephosphorization coincides, so that no excessive dephosphorization occurs.

  Further, by determining the slag evacuation rate of the intermediate evacuation in this manner, the evacuation rate is usually lower than that in the case of the first embodiment described above, that is, the slag discharge amount is reduced. Therefore, the intermediate elimination time in the third step can also be greatly shortened. That is, according to the molten steel blowing method according to the present embodiment, changing the total amount of CaO charged into the converter in the fourth step of the n charge and the second step of the (n + 1) charge. In addition, while suppressing the generation of undehydrated CaO, the intermediate evacuation time can be greatly shortened due to the decrease in the evacuation rate.

  Here, based on FIG. 5, the waste time at the time of intermediate waste between the case of the molten steel blowing method according to the first embodiment and the case of the molten steel blow method according to the present embodiment. The comparison result will be described. FIG. 5 is a graph showing an example of the relationship between the slag evacuation amount (ton) and the slag evacuation time (min) at the time of intermediate evacuation, and the vertical axis represents the slag evacuation amount (ton) and the horizontal axis Indicates the slag evacuation time (minutes). In FIG. 5, the amount of slag in the furnace in the second step was about 17 t / charge.

  In FIG. 5, ● represents the case of the first embodiment, and ▲ represents the case of the present embodiment. As can be seen, the desiliconization / dephosphorization in the second step of the (n + 1) charge is shown. By determining the slag rejection rate of the intermediate rejection in the third step of the n charge so that the required CaO amount and the CaO amount necessary for dephosphorization in the fourth step of the n charge coincide with each other. It can be seen that the excretion time is greatly reduced from about 4 minutes to about 1 minute 30 seconds.

  Next, the molten steel blowing method according to the present embodiment will be described more specifically based on FIG. The abbreviations used in FIG. 4 are the same as those used in FIG.

  When desiliconization / dephosphorization blowing (BI) of the first charge is started, an action of adding an amount of CaO necessary for desiliconization / dephosphorization blowing of the first charge is performed (W1CaO <1>). ). As a result of this desiliconization and dephosphorization, the actual results are obtained as clarified information, and at this point, the Si concentration (HM [Si] <2>) in the second charge blast furnace hot metal is also obtained as clarified information. Therefore, based on this information and information on the target slag basicity (BIC / S <2>) for desiliconization / dephosphorization blowing at the second charge, etc. The amount of CaO to be added in the first charge decarburization blowing including the amount of CaO required in phosphorus blowing (next channel required W2CaO <1>) is calculated. Along with this calculation, from the information such as the target value of P concentration in the molten steel of the first charge ([P] f <1>) and the blowout temperature target of the first charge, it is eliminated in the intermediate rejection of the first charge. The power removal amount (necessary waste amount <1>) is calculated. This required amount of waste <1> is such that the amount of CaO required for desiliconization / dephosphorization of the second charge and the amount of CaO required for dephosphorization during decarburization blowing of the first charge are the same. Calculated to satisfy. Both of these calculations are performed before intermediate exclusion.

  Next, the intermediate charge of the first charge is performed. The amount of waste (the amount of waste <1>) at this time is adjusted to match the required amount of waste <1> calculated as described above. By this intermediate rejection, information on the rejection rate (rejection rate <1>) of the first charge is found.

  After completion of the intermediate waste, decarburization blowing (BII) is started, but the amount of CaO added at this time (W2CaO <1>) is the next ch required W2CaO <1> calculated as described above. To be determined. After completion of decarburization blowing (BII), information on the amount of slag (recycled amount) to be reused for desiliconization / dephosphorization of the second charge and the components of the slag are revealed.

  Next, decarburization slag of the first charge is reused, and desiliconization / dephosphorization blowing (BI) of the second charge is started. Since the CaO necessary at this time has already been added during the decarburization blowing of the first charge, the amount of CaO (W1CaO <2>) added during the desiliconization / dephosphorization blowing of the second charge Can be zero. At this time, the results of desiliconization / dephosphorization blowing at the second charge, Si concentration (HM [Si] <3>) in the blast furnace hot metal at the third charge, and desiliconization / dephosphorization at the third charge Decarburization blowing for the second charge including the amount of CaO required for desiliconization and dephosphorization blowing for the third charge based on information on the basicity of slag (BIC / S <3>) that is the target for blowing. Calculating the amount of CaO added by smelting (next channel required W2CaO <2>) is the same as in the first charge. In this way, by repeating the steps from desiliconization / dephosphorization treatment to slag solidification, slag can be effectively used while suppressing the generation of undehydrated CaO.

  In addition, in the molten steel blowing method according to the present embodiment, when adjusting the amount of slag discharged at the time of intermediate discharge, by using the in-situ weighing of the amount of discharged slag, the generation of un-enriched CaO About the point which can further improve the precision of suppression, it is the same as that of the case of 1st Embodiment mentioned above.

Next, the effect which the molten steel blowing method which concerns on this embodiment has based on FIG. 6 is demonstrated. In addition, FIG. 6 is a graph showing an example of the content (%) of undehydrated CaO content in the slag after blowing depending on whether or not new CaO is added during desiliconization / dephosphorization blowing. The relationship is examined by taking the content (%) of the unhatched CaO content on the axis and the basicity (CaO / SiO ₂ ) on the horizontal axis.

  In general, when slag is used as a roadbed material, the expansion rate of slag is required to be 2.5% or less. In order to secure an expansion rate of 2.5% or less, It is said that it is necessary that the non-catalyzed CaO content is about 1%. On the other hand, as shown in FIG. 6, in the range of 1.0 to 2.0 basicity, which is usually a necessary condition at the time of desiliconization / dephosphorization, desiliconization / dephosphorization is performed. In the case where no new CaO was added at the time of blowing, it was found that in all cases, the undehydrated CaO content was less than 1%, and the slag quality was excellent enough to be used as a roadbed material. On the other hand, when there is a new addition of CaO at the time of desiliconization / dephosphorization, in most cases, the undehydrated CaO content in the slag exceeds 1%, and the quality of the slag may deteriorate. all right. From these results, it is possible to reduce the undehydrated CaO in the dephosphorized slag by not adding new CaO during desiliconization and dephosphorization blowing, thereby improving the quality of the slag. It was suggested that it can be made.

  Under the operating conditions shown in Table 1 below, the amount of undissolved CaO in the waste slag was examined by changing the rejection rate in the third step of the n-th charge and the amount of added CaO in the fourth step. The results are shown in Table 1. The necessary CaO amount was determined as the amount of CaO added in the fourth step of the n-th charge by adopting the larger value of the amounts calculated by the above formulas (I) and (II).

  As shown in Table 1, about the present invention examples 1-4, undissolved CaO in the waste slag of the (n + 1) charge was able to be 0.5 mass% or less.

  As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to this example. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Understood.

It is explanatory drawing which shows the outline | summary of the operating method of the converter by the method of reusing decarburization slag. It is a graph which shows an example of the relationship between the slag rejection rate (%) at the time of intermediate rejection, and the CaO addition amount (kg / t) at the time of decarburization blowing. It is explanatory drawing which shows the flow of the blowing method of the molten steel which concerns on the 1st Embodiment of this invention. It is explanatory drawing which shows the flow of the blowing method of the molten steel which concerns on the 2nd Embodiment of this invention. It is a graph which shows an example of the relationship between the amount of slag evacuation (ton) at the time of an intermediate evacuation, and slag evacuation time (minutes). It is a graph which shows the example of the content rate (%) of the non-catalyzed CaO content in the slag after the said blowing by the presence or absence of addition of new CaO at the time of desiliconization and dephosphorization blowing.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Converter 20 Ladle 30 Top blowing lance 40 Waste ladle 50 Carriage 110 Hot metal (molten steel)
130 slug

Claims (4)

A hot metal preliminary treatment step in which desiliconization and dephosphorization are carried out by blowing hot metal in a converter charged with CaO in an amount that makes the basicity of slag the target basicity, and after the hot metal preliminary treatment step An intermediate waste discharging process for discharging the slag from the converter, and a decarburizing treatment process for performing decarburization and final dephosphorization by adding CaO to the converter and blowing it, are repeated in order, n A slag after the decarburization treatment step of the charge is a molten steel blowing method for reusing the slag in the hot metal pretreatment step of the (n + 1) charge,
The amount of CaO added in the decarburization process step of the n charge is set to a CaO amount that can secure at least the target basicity in the hot metal pretreatment step of the (n + 1) charge. Blowing method.   The amount of CaO added in the n-th charge decarburization treatment step is the amount of CaO necessary for the final dephosphorization in the n-th charge decarburization treatment step and the target basicity in the (n + 1) charge hot metal pretreatment step. The molten steel blowing method according to claim 1, wherein the amount of CaO required to obtain a sufficient amount is sufficient.   The amount of slag discharged in the intermediate discharge step of the n-th charge is determined by the addition amount of CaO necessary for the final dephosphorization in the decarburization step of the n-charge and the hot metal pretreatment step of the (n + 1) -th charge. The method for blown molten steel according to claim 1 or 2, wherein the addition amount of CaO necessary for obtaining the target basicity is made equal. The amount of CaO added in the n-th charge decarburization process is the larger amount of CaO calculated from the following formula (I) or (II): The molten steel blowing method of any one of -3.
W _{P, CaO} = 1000 / Lp <n> × (B2 [P] i <n> / target [P] f <n> +1) × (% CaO) B2 <n> −R _{B1, CaO <n>.} .. (I)
W _{Si, CaO} = (HM [Si] <n + 1> × 60/28 × 10 + R _{SiO2 <n>} ) × (B1C / S <n + 1>) − R′CaO _<n> (II)
However, each parameter in the formulas (I) and (II) is as follows.
WP _{, CaO: The} amount of CaO necessary for dephosphorization in the fourth step of the n-th charge Lp <n>... Estimated phosphorus distribution in the fourth step of the n-th charge B2 [P] i <n> ..Phosphorus concentration carried over to the 4th step of the n-th charge (converted to phosphorus concentration in molten iron)
Target [P] f <n> ... target phosphorus concentration after the fourth charge of the n-th charge (% CaO) B2 <n> ... CaO in the slag after the fourth charge of the n-charge Estimated concentration R _{B1, CaO <n>} ... The amount of CaO carried over from the second step of the n-th charge to the fourth step through the third step W _{Si, CaO} . The amount of CaO to be added in the fourth step of the n-th charge necessary to secure the basicity target value in the step HM [Si] <n + 1> (n + 1) hot metal charged into the converter at the charge point from the density R _{SiO2 <n>} ··· _n charge th Si in, at (n + 1) SiO ₂ amount is recycled to the charge th B1C / S <n + 1> ··· (n + 1) charge th second step basicity target value R _{'CaO <n>} ··· _n or charge th , (N + 1) of the amount of CaO to be recycled to the charge eyes, CaO amount excluding the amount to be added by n charge th fourth step

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