JP2018188730A - Converter steelmaking process - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decrease the phosphor concentration in molten steel to be smelted and to simultaneously improve the productivity and dissolution efficiency of the cold iron source in a converter steelmaking method for smelting molten steel from hot metal using one converter.SOLUTION: The converter steelmaking method according to the present invention comprises: a first process of charging hot metal into a converter; a second process of supplying a CaO-based solvent to the converter for hot metal desiliconization in the converter; a third process of discharging at least a part of slag generated in the second process from the converter; a fourth process of supplying a CaO-based solvent to the converter and dephosphorization of the hot metal left in the converter; a fifth process of discharging at least a part of slag generated in the fourth process from the converter; and a sixth process of supplying a CaO-based solvent to the converter to decarbonize the hot metal left in the converter. A subsequent first process of the next charge is carried out in the state where the slag generated in the sixth process is left in the converter. The slag generated in the sixth step is re-used as the CaO-based solvent for the desiliconization treatment in the next charge.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a converter steelmaking method in which hot metal charged in a converter is subjected to oxygen blowing to produce molten steel from the hot metal.

  In order to reduce the amount of steelmaking slag and improve the quality of the molten steel, pretreatment of desiliconization, dephosphorization, and desulfurization is performed on the hot metal before decarburizing and refining in the converter. . Among them, in the hot metal dephosphorization treatment using a converter, the oxygen gas supply flow rate (also referred to as “acid feed rate”) can be increased, and high-speed treatment is possible. On the other hand, when increasing the production amount of molten steel, since the preliminary treatment is originally performed using the converter used for decarburization refining, the dephosphorization treatment of the hot metal using the converter becomes difficult.

  In order to reduce the amount of carbon dioxide generated in the steel making process, it is effective to mix a cold iron source as an iron source to reduce the hot metal ratio. The converter equipment can use a scrap chute or the like to input a large amount of cold iron source, but heat compensation for melting the cold iron source is required for refining in the converter.

  The hot metal dephosphorization treatment is performed by adding a CaO-based solvent such as quicklime while feeding the acid, but the carbon in the hot metal is also oxidized and removed, resulting in a decrease in the latent heat of the hot metal. Therefore, on the premise of not adding an exothermic material such as an expensive Fe-Si alloy in decarburization refining in a converter, promote melting of a cold iron source without performing dephosphorization treatment on hot metal, It is necessary to select whether to carry out dephosphorization treatment.

  Conventionally, Patent Document 1 and Patent Document 2 describe desiliconization / dephosphorization treatment and decarburization refining in order to rationalize both hot metal dephosphorization in a converter and melting of a cold iron source. There has been proposed a converter steelmaking method that is continuously performed in one converter with an exhausting step of exhausting slag generated by the dephosphorization process. In this refining method, after desiliconization and dephosphorization, the converter is tilted and exhausted, and then decarburization refining is carried out, and the slag after decarburization refining remains in the furnace and the molten iron of the next charge is charged. Then, desiliconization / dephosphorization processing for the next charge has started.

  On the other hand, in Patent Document 3, Patent Document 4, Patent Document 5, and Patent Document 6, in the hot metal pretreatment using the converter, the slag produced by the desiliconization process by tilting the converter after the first half of the desiliconization process. Next, the CaO-based solvent is added to the hot metal and the slag after the desiliconization process left in the converter, and the dephosphorization process of the hot metal is performed by blowing oxygen gas. Pre-processing methods have been proposed. Note that the refining method disclosed in Patent Documents 1 to 6, in which slag in the furnace is once discharged and new slag is formed in the furnace is also referred to as “double slag method”.

Patent Document 7 discloses a first step of charging a cold iron source and hot metal into the converter for the purpose of improving the efficiency of melting the cold iron source in the converter steelmaking process, and desiliconization treatment by blowing oxygen gas into the converter. And a second step of performing decarburization refining, and then a third step of stopping the blowing of oxygen gas and charging a cold iron source having a specific surface area of 0.5 to 11.0 m ² / ton into the converter, Next, a refining method has been proposed which includes a fourth step in which quick lime is charged into the converter and oxygen gas is blown into the converter to perform decarburization refining and dephosphorization at the same time, and further, steel is removed. That is, a technique has been proposed in which a cold iron source is charged twice into the converter by one converter refining.

JP 2000-328123 A JP 2001-192720 A JP 2013-189714 A International Publication No. 2013/012039 JP 2013-231237 A JP 2013-227664 A JP 2013-133484 A

  However, the above prior art has the following problems.

  That is, in the case of desiliconization / dephosphorization treatment → exhaust process → decarburization refining in which double slag method is applied to the converter steelmaking method disclosed in Patent Documents 1 and 2, the first half of desiliconization / dephosphorization The problem is that the phosphorus concentration of the molten steel is difficult to reduce in the latter half of the decarburization refining because the phosphorus concentration of the hot metal is not sufficiently reduced at the treatment stage and exhaustion cannot be performed completely. There is.

  On the other hand, in the case of desiliconization → exhaust → dephosphorization, in which the double slag method is applied to the hot metal pretreatment disclosed in Patent Documents 3 to 6, the phosphorus concentration in the hot metal after dephosphorization is lowered. In addition, since decarburization and refining is performed in a separate converter, it is possible to reduce the phosphatization of molten steel. However, since two converters are used, there is a problem that productivity is low. is there.

  According to the technology disclosed in Patent Document 7 in which a cold iron source is charged twice in a converter, a low basicity and high viscosity slag generated by desiliconization in the furnace when the cold iron source is charged for the second time. Therefore, there is a problem that the charged cold iron source is coated with the slag in the furnace and the melting efficiency during refining is lowered.

  The present invention has been made in view of the above circumstances. The object of the present invention is to use a single converter, perform oxygen blowing on the hot metal charged in the converter, and smelt the molten steel from the hot metal. In the converter steelmaking method, the phosphorus concentration of the molten steel to be melted can be lowered, and at the same time, the converter steelmaking method capable of increasing the productivity of the converter and the melting efficiency of the cold iron source is provided. is there.

The gist of the present invention for solving the above problems is as follows.
[1] A converter steelmaking method in which hot metal is refined from a hot metal in one converter and a molten steel is produced from the hot metal, the first step of charging the hot metal into the converter, and a CaO-based medium in the converter. A second step of supplying a solvent, and agitating the hot metal in the converter with the bottom blowing gas, supplying oxygen gas from the top blowing lance to the hot metal, and desiliconizing the hot metal in the converter; A third step of tilting and discharging at least a part of the slag generated in the second step from the converter; returning the converter to an upright position; supplying a CaO-based solvent to the converter; A fourth step of dephosphorizing the hot metal remaining in the converter by supplying oxygen gas from the top blowing lance to the hot metal while stirring the hot metal in the bottom blowing gas; and fourth tilting the converter again. A fifth step of discharging at least a part of the slag generated in the process from the converter, and returning the converter to an upright position, Supplying an O-based solvent and stirring the hot metal in the converter with the bottom blowing gas while supplying oxygen gas from the top blowing lance to the hot metal to decarburize and refine the hot metal remaining in the converter The first step of the next charge is performed with the slag generated in the sixth step remaining in the converter, and the slag generated in the sixth step is desiliconized by the next charge. A converter steelmaking method for reuse as a CaO-based solvent.
[2] The converter steelmaking method according to [1], wherein the slag discharged in the third step and the slag discharged in the fifth step are discharged into the same slag holding container.
[3] Before the molten iron is charged into the converter in the first step, after the third step, and at least one of the periods after the fifth step, the cold iron source is loaded into the converter. The converter steelmaking method according to [1] or [2] above.
[4] Before the molten iron is charged into the converter in the first step, the cold iron source is charged into the converter, and further, after the third step and / or after the fifth step, into the converter. The converter steelmaking method according to [1] or [2] above, wherein a cold iron source is charged.
[5] Before the molten iron is charged into the converter in the first step, after the third step, and after the fifth step, the amount of cold iron source charged in each period The converter steelmaking method according to the above [3] or [4], wherein the total iron source to be charged is 10 mass% or less.

  According to the present invention, in a converter steelmaking method in which molten steel is melted from hot metal in a single converter, desiliconization treatment, dephosphorization treatment and decarburization refining are performed separately, and desiliconization treatment and dephosphorization are performed. After the treatment, each slag is discharged and slag is formed three times in the furnace, which promotes the discharge of phosphorus contained in the hot metal to the outside of the furnace and stabilizes the phosphorus concentration in the molten steel after decarburization refining. Can be realized. In addition, decarburization slag generated by decarburization refining is left in the furnace and reused as the CaO source for the next charge desiliconization treatment, so the slag discharged outside the system is desiliconized slag and dephosphorized slag. The amount of heat and iron content of the decarburized slag from the previous charge can be recovered in the desiliconization process of the next charge. Dissolution is promoted, and the iron yield is improved by the recovered iron. Furthermore, in the present invention, since a single converter is used to refine the molten metal in the furnace without discharging it outside the furnace, a reduction in the productivity of the converter is suppressed.

  In the present invention, the cold iron source can be added in a plurality of times, the dissolution of the cold iron source is promoted, and the carbon dioxide generation amount is reduced.

It is a schematic sectional drawing of the converter used when implementing the converter steelmaking method which concerns on this invention. It is the schematic which shows the converter steelmaking method which concerns on this invention in process order.

  Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a schematic cross-sectional view of a converter used when the converter steelmaking method according to the present invention is carried out, and FIG. 2 is a schematic diagram showing the converter steelmaking method according to the present invention in the order of steps. In addition, FIG. 1 is a figure which shows the desiliconization process of the 2nd process of FIG. 2- (C).

  In the converter steelmaking method according to the present invention, a converter 1 capable of blowing an upper bottom as shown in FIG. 1 is used. The top blowing is performed by supplying an oxygen-containing gas toward the hot metal 5 as an oxygen source from the tip of the top blowing lance 2 via the top blowing lance 2 that can move up and down in the converter 1. As the oxygen-containing gas, oxygen gas, oxygen-enriched air, air, or a mixed gas of oxygen gas and inert gas can be used. FIG. 1 shows an example in which oxygen gas 8 is used as the oxygen-containing gas. Here, the oxygen gas 8 is industrial pure oxygen. The bottom blowing is performed through a bottom blowing tuyere 3 provided at the bottom of the converter 1. The bottom blowing gas 9 may be a gas containing oxygen gas or only an inert gas such as argon gas or nitrogen gas. By blowing into the hot metal, the stirring of the hot metal 5 is strengthened to promote the melting of the cold iron source. It is sufficient if it has a function to perform.

  In the present invention, one converter 1 is used for refining the hot metal 5, the desiliconization treatment and the dephosphorization treatment of the hot metal preliminary treatment are performed, and the waste after the desiliconization treatment and after the dephosphorization treatment is performed. Further, decarburization refining is performed on the hot metal that has been subjected to the dephosphorization treatment, and molten steel is produced from the hot metal.

  In the converter steelmaking method according to the present invention, a cold iron source 7 is charged into the converter 1 via a scrap chute 10 as shown in FIG. In the present invention, it is essential that the slag produced by the decarburization and refining of the pre-charge performed in the converter 1 (referred to as “decarburized slag”) remains in the converter, and therefore the decarburized slag remains. Although the cold iron source 7 will be charged into the converter 1, FIG. 2- (A) shows the state of the first charge when the operation such as after the periodic repair is started (the decharged slag of the previous charge is It indicates a state that does not exist.

  Although charging the cold iron source 7 into the converter 1 is not an essential condition for carrying out the present invention, the converter 1 of the cold iron source 7 is used to reduce the amount of carbon dioxide generated in the steelmaking process. It is preferable to perform charging.

  Next, as shown in FIG. 2-(B), the hot metal 5 (hereinafter referred to as “blast furnace hot metal 5”, which is discharged from the blast furnace through the charging pot 11 and subjected to desulfurization treatment as required, is converted into the converter 1. ”) (First step).

Thereafter, oxygen gas 8 is supplied as an oxygen source to the blast furnace hot metal 5 in the converter, and desiliconization processing is performed as shown in FIG. 2- (C) (second step). Silicon contained in the blast furnace hot metal 5 reacts with oxygen in the oxygen source (Si + 2O → SiO ₂ ), and desiliconization proceeds. The hot metal temperature rises due to the oxidation heat of silicon by this desiliconization reaction, and the dissolution of the cold iron source 7 in the hot metal is promoted.

In the present invention, the decarburized slag generated by the precharge decarburization refining performed in the converter 1 is left in the converter as a CaO source, and the SiO ₂ generated by the desiliconization reaction is generated in the furnace. The slag 6 is produced by reacting with the pre-charged decarburized slag. Since the slag 6 generated in the desiliconization process is also referred to as “desiliconization slag”, the slag 6 generated in the desiliconization process is hereinafter referred to as “desiliconization slag 6”.

In the desiliconization treatment, the basicity ([mass% CaO] / [mass% SiO ₂ ]) (hereinafter sometimes simply referred to as “basicity”) of the desiliconization slag 6 is 0.5 or more, preferably Is kept above 0.8. The reason for controlling the basicity of the desiliconized slag 6 to 0.5 or more is that when the basicity of the desiliconized slag 6 is less than 0.5, it was contained in the decarburized slag of the pre-charge during the desiliconization process. The phosphorous oxide 3CaO · P ₂ O ₅ is decomposed, and the decomposed phosphorus returns to the blast furnace hot metal 5 (this phenomenon is referred to as “rebound phosphorus”), and the phosphorus concentration in the hot metal 14 after the desiliconization treatment is higher than that before the desiliconization treatment. Because it happens to be high. As the basicity of the desiliconized slag 6 increases, dephosphorization does not occur. Therefore, the basicity of the desiliconized slag 6 is preferably set to 0.8 or more.

The precharged decarburized slag remaining in the furnace is diluted with SiO ₂ produced by the desiliconization treatment, and the basicity of the desiliconized slag 6 produced in the furnace is gradually lowered, but the precharge remaining Since the basicity of the decarburized slag is as high as 2.5 to 5.0, the basicity of the desiliconized slag 6 produced in the furnace is normally secured to 0.5 or more.

  However, in the case of the first charge after the start of operations such as after periodic repairs, the pre-charged decarburized slag does not remain in the furnace, so the basicity of the desiliconized slag 6 is adjusted to 0.5 or more. It is necessary. Further, even when the pre-charged decarburized slag remains, there may be a case where the basicity of the desiliconized slag 6 must be adjusted to 0.5 or more.

  Thus, when adjusting the basicity of the desiliconization slag 6 to 0.5 or more, a CaO-based solvent is added to the converter 1 before and / or during the desiliconization process. The addition amount of the CaO-based solvent need not be excessively increased, and the upper limit of the basicity of the desiliconized slag 6 may be about 1.5.

  As the CaO-based solvent in the desiliconization treatment, quick lime, dolomite, calcium carbonate and the like can be used. In addition, the decarburized slag can be cooled and solidified, and the solidified decarburized slag can be crushed or can be used as a CaO-based solvent without crushed or in bulk or powder.

  As an oxygen source for the silicon removal treatment, only the oxygen gas 8 from the top blowing lance 2 may be used, or iron oxide (not shown) may be used in combination with the oxygen gas 8. In order to form the desiliconized slag 6 having a target basicity during the desiliconization process performed in a short time, it is effective to use iron oxide having a function of promoting the hatching of the CaO-based solvent. However, in the present invention, since decarburized slag in a molten state is used as the CaO-based solvent, even if desiliconization treatment is performed using only the oxygen gas 8, a sufficiently targeted basic desiliconized slag. 6 can be formed. Furthermore, since the converter 1 capable of strong stirring is used as the refining vessel, the desiliconized slag 6 having a sufficiently basic basicity can be formed even if only the oxygen gas 8 is used.

After this desiliconization treatment, as shown in FIG. 2- (D), the converter 1 is tilted to provide an exhausting step, and the desiliconization slag 6 containing a large amount of SiO ₂ generated by the desiliconization treatment. Is discharged from the furnace port of the converter 1 to a slag holding container (not shown) (third step).

In order to discharge SiO ₂ generated by the desiliconization process to the outside of the furnace as much as possible, the rejection rate (rejection rate (mass%) = (discharge slag mass) x 100 / (in-furnace slag mass at the end of desiliconization process)) ) Is preferably 50% by mass or more. In order to ensure a rejection rate of 50% by mass or more, the basicity of the desiliconized slag 6 is adjusted to a range of 0.5 to 1.1, and the temperature of the desiliconized slag 6 is adjusted to 1280 ° C. or higher. It is preferable.

  After the desiliconization slag 6 is discharged, the converter 1 is returned to an upright position with the furnace port facing upward, and the desiliconized hot metal 14 (hereinafter referred to as “desiliconized hot metal 14”) left in the converter. 2), a dephosphorization treatment is performed on the desiliconized hot metal 14 as shown in FIG. 2- (E) (fourth step). Since the slag generated in the dephosphorization process is also referred to as “dephosphorization slag”, the slag 12 generated in the dephosphorization process is hereinafter referred to as “dephosphorization slag 12”.

In the dephosphorization treatment, the basicity of the dephosphorization slag 12 in the furnace is adjusted to a range of 1.5 to 3.5. The higher the basicity of the dephosphorization slag 12, the higher the absorption capacity of the phosphor oxide (3CaO · P ₂ O ₅ ), and the dephosphorization reaction is promoted. Therefore, in order to promote the dephosphorization reaction, the dephosphorization slag 12 The basicity is controlled to 1.5 or more. On the other hand, if the basicity of the dephosphorized slag 12 exceeds 3.5, the hatchability of the dephosphorized slag 12 is deteriorated and the dephosphorization reaction is slowed, so the basicity of the dephosphorized slag 12 is set to 3.5 or less. Control.

  Examples of the CaO-based solvent used in the dephosphorization treatment include quick lime, dolomite, and calcium carbonate. However, it is not limited to these, What contains 50 mass% or more of CaO, and also contains other components, such as a fluorine and an alumina as needed, can be used as a CaO type | system | group solvent solvent at the time of a dephosphorization process. . As a method for adding the CaO-based medium solvent, granular and lump-shaped ones can be charged from a hopper on the furnace, and powdery ones can be charged through an upper blowing lance 2 or the like.

  The oxygen source used in this dephosphorization process is mainly composed of the oxygen gas 8 from the top blowing lance 2 as in the desiliconization process, but a part of iron oxide may be used.

Phosphorus contained in the desiliconized hot metal 14 is oxidized to oxygen in the supplied oxygen source to become phosphorus oxide (P ₂ O ₅ ), which is formed by the incubation of the CaO-based solvent, and dephosphorized. The dephosphorization slag 12 functioning as a refining agent is incorporated as a stable compound of 3CaO · P ₂ O ₅ , and the dephosphorization reaction of the desiliconized hot metal 14 proceeds. When the dephosphorization reaction proceeds and the phosphorus concentration in the desiliconized molten iron 14 is lowered to a predetermined value, the dephosphorization process is terminated.

  In order to stably lower the phosphorus concentration of the molten steel produced by the decarburization and refining in the subsequent process, the phosphorus concentration of the hot metal 15 after the dephosphorization treatment (hereinafter referred to as “dephosphorized hot metal 15”) is set to 0. It is preferable to perform a dephosphorization process until it becomes 040 mass% or less.

After this dephosphorization treatment, as shown in FIG. 2 (F), the converter 1 is tilted again to provide an exhausting step, and contains 3CaO · P ₂ O ₅ generated by the dephosphorization treatment. At least a part of the dephosphorization slag 12 is discharged from the furnace port of the converter 1 to a slag holding container (not shown) (fifth step).

  At that time, it is preferable that the desiliconized slag 6 is discharged in the third step, and the dephosphorized slag 12 is discharged into a slag holding container containing the desiliconized slag 6. By recovering the desiliconized slag 6 and the dephosphorized slag 12 in the same slag holding container, the logistics in the converter plant is simplified and efficient operation can be performed.

In order to discharge 3CaO · P ₂ O ₅ generated in the dephosphorization process outside the furnace as much as possible, the rejection rate (rejection rate (mass%) = (discharge slag mass) × 100 / (furnace at the end of dephosphorization process) The inner slag mass)) is preferably 50% by mass or more.

  After the dephosphorization slag 12 is discharged, the converter 1 is returned to the upright position with the furnace port facing upward, and the dephosphorization molten iron 15 remaining in the converter is added to the CaO-based solvent and oxygen source. As shown in FIG. 2 (G), decarburization refining is performed on the dephosphorized molten iron 15 (sixth step).

  In decarburization refining, the basicity of the slag 13 in the furnace is adjusted to 2.5 to 5.0. This is because in decarburization refining, it is necessary to dephosphorize the dephosphorized hot metal 15 obtained by the dephosphorization treatment to a lower concentration than that of the dephosphorization treatment. It is also necessary to increase it. On the other hand, decarburization refining has a higher flow rate of oxygen gas blown than dephosphorization and strong stirring of the molten metal, so if the basicity is 5.0 or less, the slag 13 in the furnace will sufficiently hatch. . Since the slag generated in the decarburization refining is also referred to as “decarburization slag”, the slag 13 generated in the decarburization refining is hereinafter referred to as “decarburization slag 13”.

  As the CaO-based solvent used for decarburization refining, quick lime, dolomite, calcium carbonate and the like can be used. However, it is not limited to these, What contains 50 mass% or more of CaO, and also contains other components, such as a fluorine and an alumina as needed, can be used as a CaO type | system | group solvent at the time of decarburization refining. . As a method for adding the CaO-based medium solvent, granular and lump-shaped ones can be charged from a hopper on the furnace, and powdery ones can be charged through an upper blowing lance 2 or the like. Further, the oxygen source used in the decarburization refining mainly includes oxygen gas 8 from the top blowing lance 2.

  After decarburization refining, as shown in FIG. 2 (H), the converter 1 is tilted to the side where the outlet 4 is installed, and the molten steel 16 in the molten converter is passed through the outlet 4. Steel is discharged into a molten steel holding container (not shown) such as a ladle.

  After the molten steel 16 is discharged, the decarburized slag 13 in the furnace is left without being discharged, and the cold iron source 7 is charged into the converter 1 as shown in FIG. As shown in (B), the blast furnace hot metal 5 is charged into the converter 1 and the next charge desiliconization process is started. The decarburized slag 13 left in the furnace is effectively used as a CaO source in the next charge desiliconization process. When a part of the decarburized slag 13 is exhausted, the processing time is increased by the amount of the exhaust time, and the productivity of the converter 1 is reduced. To avoid this, the exhaust of the decarburized slag 13 is reduced. It is preferable not to perform the soot treatment. That is, it is preferable to leave the entire amount of the decarburized slag 13 in the furnace.

  In the converter steelmaking method according to the present invention, it is preferable to charge as many cold iron sources 7 as possible in order to improve productivity and reduce carbon dioxide emission. From this point of view, before the molten iron is charged into the converter in the first step, after the third step, at least one of the periods after the fifth step, the cold iron source is supplied into the converter. It is preferable to charge. In particular, as described above, the cold iron source 7 is charged into the converter 1 before the blast furnace hot metal 5 is charged into the converter 1 in the first process, and further, in the desiliconization process (second process). After the third step of discharging the generated desiliconized slag 6 and / or after the fifth step of discharging the dephosphorized slag 12 generated in the dephosphorization process (fourth step), cooling is performed in the converter. More preferably, the iron source 7 is charged. The charging amount of the cold iron source into the converter is preferably 10% by mass or less of the total iron source charged into the converter in any period from the viewpoint of suppressing undissolution of the cold iron source. . Even when the total charging amount of the cold iron source 7 is the same, melting the cold iron source 7 is promoted by dispersing and charging the cold iron source 7. Here, the total iron source is the sum of the mass of the hot metal charged into the converter and the mass of the cold iron source in the charge.

  Moreover, when increasing the charging amount of the cold iron source 7, it is preferable to use the combustion heat of silicon contained in the blast furnace hot metal 5 for melting the cold iron source 7. Therefore, in that case, it is desirable not to perform the desiliconization process in the blast furnace casting floor.

  As described above, according to the present invention, the desiliconization process, the dephosphorization process, and the decarburization refining are separately performed in the converter steelmaking method in which the molten steel 16 is melted from the blast furnace hot metal 5 in one converter 1. In addition, after the desiliconization process and the dephosphorization process, the waste is exhausted and the slag is formed three times in the furnace (triple slag method), so that the phosphorus contained in the blast furnace hot metal 5 is discharged to the outside of the furnace. Emission is promoted, and it becomes possible to stably realize low phosphorusization of the molten steel 16 after decarburization refining, which was a problem when the double slag method is applied to the converter steelmaking method. In addition, the decarburized slag 13 generated by decarburization refining is left in the furnace and reused as the CaO source for the next charge desiliconization treatment. It becomes only phosphorus slag 12 and not only the discharge amount of slag is reduced, but also the amount of heat and iron content of the decarburization slag 13 of the previous charge can be recovered in the desiliconization process of the next charge, and depending on the amount of recovered heat The melting of the cold iron source 7 is promoted, and the iron yield is improved by the recovered iron content. Furthermore, in this invention, since the molten metal in a furnace is refined using one converter 1 without discharging | emitting outside a furnace, the fall of the productivity of the converter 1 is suppressed.

  The converter steelmaking method according to the present invention was carried out using a converter having a capacity of 300 tons as shown in FIG. 1 (Invention Example 1). In addition, for comparison purposes, the waste will be discharged only once after the dephosphorization treatment. After the dephosphorization treatment, the dephosphorization molten iron is poured out and charged into another converter for decarburization or refining. The test operation (Comparative Examples 1-3) which does not reuse charcoal slag was also implemented.

  In Table 1, the supply conditions of the top blown oxygen gas and the bottom blown nitrogen gas for stirring in the desiliconization treatment using the converter, the dephosphorization treatment, and the decarburization refining in Invention Example 1 and Comparative Examples 1 to 3, Blowing time indicates the mass of hot metal to be refined.

  Table 2 shows the test conditions of Example 1 of the present invention and Comparative Examples 1 to 3. As shown in Table 2, the present invention example 1 and comparative examples 1 to 3 were tested without charging a cold iron source.

  Comparative Example 1 is a double slag method of desiliconization / dephosphorization → waste removal → decarburization refining, and Comparative Example 2 is desiliconization → waste → dephosphorization → tapping → recharging to another converter → The double slag method of decarburization refining, Comparative Example 3 is a triple slag method of desiliconization treatment → exhaust → dephosphorization → exhaust → decarburization refining, but is a condition in which decarburization slag is not reused . Invention Example 1 is a triple slag method of desiliconization treatment → exhaust → dephosphorization → exhaust → decarburization refining, and the decarburization slag is left in the converter without being exhausted. Charged hot metal was charged and the remaining decarburized slag was reused in the next charge desiliconization process. Further, in Invention Example 1, the desiliconized slag and the dephosphorized slag were discharged into the same slag holding container.

  Table 3 shows metallurgical properties, productivity, and CaO-based solvent basic units in Invention Example 1 and Comparative Examples 1 to 3. Table 3 shows the average value of 20 charges in each test, and the total processing time in Table 3 is the time from the hot metal charging at the start of refining to the end of the final decarburization refining, steel output, and exhausting.

  Comparative Example 1 is only the waste after desiliconization / dephosphorization treatment, and therefore the total treatment time is short. However, since the phosphorus concentration in the hot metal after the desiliconization and dephosphorization treatment was high (0.055% by mass) and the rejection rate was 60% by mass, it remained in the furnace during decarburization and refining. The amount of phosphorus to be carried out was large, and the phosphorus concentration of the molten steel after decarburization refining was high (0.012% by mass).

  In Comparative Example 2, in addition to the waste after the desiliconization treatment, the hot water is discharged after the dephosphorization treatment, and the dephosphorization molten iron is charged again into another converter. Therefore, the total treatment time is long. It was. However, the dephosphorization of the dephosphorized hot metal was made low by the dephosphorization treatment, and the dephosphorization slag was almost completely removed outside the furnace, so that the phosphorus concentration in the molten steel after decarburization refining was low.

  Comparative Example 3 is a triple slag method, and the total processing time is longer than that of Comparative Example 1, but the total processing time is shorter than that of Comparative Example 2 in which tapping and recharging is performed. Moreover, the dephosphorization hot metal is low-phosphorus, and although the removal rate of dephosphorization slag is low compared with Comparative Example 2 in which dephosphorization slag is almost completely removed outside the furnace, the molten steel after decarburization refining is low. Concentration was realized. However, since the slag was not reused, the quicklime basic unit was as high as 28 kg / molten steel-t.

  Compared with Comparative Examples 1 to 3, the present invention example 1 has the same metallurgical characteristics as Comparative Example 3, and the decarburized slag is reused for the desiliconization treatment, so the quick lime unit is 25 kg / molten steel-t. And low. Moreover, since the decarburized slag was not discharged, the total processing time was shortened by that amount compared with Comparative Example 3.

  Next, the test which compares the melt | dissolution condition of a cold iron source by changing the charging time and charging amount of a cold iron source to the converter was done (invention examples 2-8).

  The refining method was the same as Example 1 of the present invention, and was a triple slag method of desiliconization treatment → removal → dephosphorization treatment → removal → decarburization refining, and the decarburization slag was reused for desiliconization treatment. In Invention Examples 2 to 8, the amount of the cold iron source charged was constant at 25% by mass of the total iron source charged in the converter. In other words, the total iron source was 300 tons, and 75 tons of cold iron source was charged per charge for 225 tons of blast furnace hot metal per charge. Of the 75 tons of cold iron source, 45 tons of cold iron source for 60% by mass is obtained by cutting waste scraps having a thickness of 10 mm or more, and the remaining 30 tons for 40% by mass is thick. A lightweight scrap having a thickness of less than 10 mm was used. Table 4 shows charging conditions of the cold iron source in Examples 2 to 8 of the present invention.

  As shown in Table 4, in melting the cold iron source for a total of 25% by mass of the total iron source, in Example 2 of the present invention, 5% by mass (lightweight scrap = 15 tons) 10% by mass (lightweight waste = 15 tons, heavy waste = 15 tons) after discharging silica slag, and 10% by weight (heavy waste = 30 tons) cold iron source in the converter after discharging dephosphorization slag. I entered.

  In Invention Example 3, 75 tons of all cold iron sources were charged into the converter before charging the blast furnace hot metal. In Invention Example 4, 15% by mass (lightweight scrap) was charged before charging the blast furnace hot metal. = 30 tons, heavy waste = 15 tons), 10% by mass (heavy waste = 30 tons) of cold iron source was charged into the converter after the desiliconization slag was discharged.

  In Example 5 of the present invention, 10% by mass (lightweight waste = 15 tons, heavy waste = 15 tons) before charging the blast furnace hot metal, and 15% by weight (lightweight waste = 15 tons, heavy waste = 30 tons) of cold iron source was charged into the converter. In Example 6 of the present invention, 5% by mass (weight waste = 15 tons) before charging the blast furnace hot metal, and 15% by mass after desiliconization slag was discharged. (Lightweight waste = 15 tons, heavy waste = 30 tons) After discharge of dephosphorization slag, 5 mass% (lightweight waste = 15 tons) of cold iron source was charged into the converter.

  In Example 7 of the present invention, 5% by mass (heavy scrap = 15 tons) before charging the blast furnace hot metal, 5% by mass (lightweight scrap = 15 tons) after discharging the desiliconized slag, and 15% after discharging the dephosphorized slag. A cold iron source of mass% (lightweight scrap = 15 tons, heavy scrap = 30 tons) was charged into the converter, and in Example 8 of the present invention, 15 mass% (lightweight scrap = 15 tons) before charging the blast furnace hot metal. , Heavy waste = 30 tons), 5 mass% (lightweight waste = 15 tons) after removal of desiliconized slag, and 5 mass% (heavy waste = 15 tons) cold iron source after removal of dephosphorization slag I was charged inside.

  In Invention Example 3, an undissolved cold iron source was confirmed at the bottom of the furnace when the converter was tilted at the time of discharge after desiliconization and at the time of discharge after dephosphorization. In addition, after steel removal after decarburization refining, an undissolved cold iron source was confirmed by mixing with decarburized slag left in the furnace.

  In Invention Example 4 and Invention Example 5, as in Invention Example 3, a part of the undissolved cold iron source is present at the bottom of the furnace at the time of discharge after the desiliconization process and at the time of discharge after the dephosphorization process. Observed. In addition, after steel removal after decarburization refining, a small amount of undissolved cold iron source was observed mixed with slag left in the furnace.

  In Invention Example 6 to Invention Example 8, compared with Invention Example 4 and Invention Example 5, although the residual amount of the cold iron source is small, it remains in the furnace after the bottom of the furnace or after steel removal after decarburization refining. A slight amount of undissolved cold iron mixed with the slag was confirmed.

  On the other hand, in Example 2 of the present invention, the decarburization slag left in the furnace at the time of exhaustion after the desiliconization process, at the time of exhaustion after the dephosphorization process, and after steel removal after the decarburization refining is not No source of dissolved cold iron was identified.

  In this way, even when the same amount of cold iron source is charged, by dispersing the charging time of the cold iron source, the cold iron by adhering the undissolved cold iron source to the furnace bottom or mixing with the slag It was found that undissolved source was reduced. Even when the cold iron source is dispersed, the amount exceeding 10% by mass of the total iron source in each step, that is, after the hot metal charging, after the desiliconization treatment, and after the dephosphorization treatment. When the cold iron source is charged, the undissolved cold iron source adheres to the furnace bottom and the cold iron source is not melted by mixing with the slag. Therefore, the amount of the cold iron source charged into the converter before the hot metal charging, after the desiliconization treatment, and after the dephosphorization treatment is 10% by mass of the total iron source in any period. It was confirmed that the following control is preferable. In addition, the metallurgical characteristics of the desiliconization reaction, the dephosphorization reaction, and the decarburization reaction in Invention Example 2 to Invention Example 8 where the dissolution behaviors of the cold iron sources were compared were the same as in Invention Example 1.

DESCRIPTION OF SYMBOLS 1 Converter 2 Top blowing lance 3 Bottom blowing tuyere 4 Outlet 5 Blast furnace hot metal 6 Desiliconization slag 7 Cold iron source 8 Oxygen gas 9 Bottom blowing gas 10 Scrap chute 11 Charging pan 12 Dephosphorization slag 13 Decarburization slag 14 Desorption Silica hot metal 15 Dephosphorized hot metal 16 Molten steel

Claims (5)

A converter steelmaking method in which hot metal is refined in one converter to produce molten steel from hot metal,
A first step of charging hot metal into the converter;
First, a CaO-based solvent is supplied into the converter, and the hot metal in the converter is desiliconized by supplying oxygen gas from the top blowing lance to the hot metal while stirring the hot metal in the converter with the bottom blowing gas. Two steps,
A third step of tilting the converter and discharging at least part of the slag generated in the second step from the converter;
Return the converter to the upright position, supply CaO-based solvent into the converter, and supply oxygen gas to the hot metal from the top blowing lance while stirring the hot metal in the converter with the bottom blowing gas. A fourth step of dephosphorizing the hot metal remaining in
A fifth step of tilting the converter again and discharging at least part of the slag generated in the fourth step from the converter;
Return the converter to the upright position, supply CaO-based solvent into the converter, and supply oxygen gas to the hot metal from the top blowing lance while stirring the hot metal in the converter with the bottom blowing gas. A sixth step of decarburizing and refining the hot metal remaining in
Consists of
The first step of the next charge is performed with the slag generated in the sixth step remaining in the converter, and the slag generated in the sixth step is reused as a CaO-based solvent by the desiliconization treatment of the next charge. Converter steelmaking method to be used.   The converter steelmaking method according to claim 1, wherein the slag discharged in the third step and the slag discharged in the fifth step are discharged into the same slag holding container.   Before charging the hot metal into the converter in the first step, after the third step, at least one of the periods after the fifth step, the cold iron source is charged into the converter. The converter steelmaking method according to claim 1 or 2.   Before the molten iron is charged into the converter in the first step, the cold iron source is charged into the converter, and after the third step and / or after the fifth step, the cold iron is put into the converter. The converter steelmaking method according to claim 1 or 2, wherein a source is charged.   Before charging the hot metal into the converter in the first step, after the third step, and after the fifth step, the amount of cold iron source charged in each period is charged into the converter in any period. The converter steelmaking method according to claim 3 or 4, wherein the total iron source is 10 mass% or less.

Images