JP6665884B2 - Converter steelmaking method - Google Patents

Description

  The present invention relates to a converter steelmaking method for smelting molten steel from hot metal by oxygen-blowing hot metal charged in a converter.

  To reduce the amount of steelmaking slag generated and improve the quality of molten steel, pretreatment of desiliconization, dephosphorization, and desulfurization is performed on hot metal before decarburization and refining in a converter. . Among them, in the dephosphorization treatment of hot metal using a converter, the supply flow rate of oxygen gas (also referred to as “acid supply 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 a 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 steelmaking process, it is effective to mix a cold iron source as an iron source to lower the hot metal ratio. The converter equipment can supply a large amount of cold iron source using a scrap chute or the like, but heat compensation for melting the cold iron source is required for refining in the converter.

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

  Conventionally, Patent Documents 1 and 2 disclose desiliconization / dephosphorization treatment and decarburization refining, and desiliconization / 2. Description of the Related Art A converter steelmaking method has been proposed in which a slag generated by a dephosphorization treatment is continuously discharged in one converter with a discharge step interposed therebetween. In this refining method, after the desiliconization and dephosphorization treatment, the converter is tilted to discharge the waste, followed by decarburization refining, and the slag after the decarburization refining remains in the furnace to charge the hot metal of the next charge Then, desiliconization and dephosphorization of the next charge is started.

  On the other hand, Patent Literature 3, Patent Literature 4, Patent Literature 5, and Patent Literature 6 disclose, in a pretreatment of hot metal using a converter, slag generated by desiliconization by tilting the converter after the first half of desiliconization. Of the hot metal after the desiliconization treatment and the slag remaining in the converter are subjected to a dephosphorization treatment of the hot metal by blowing an oxygen gas and blowing oxygen gas. A pre-treatment method has been proposed. 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 a converter, and a desiliconization treatment by blowing oxygen gas in order to improve the efficiency of melting the cold iron source in the converter steelmaking process. And a second step of performing decarburization refining, and then a third step of stopping the supply of oxygen gas and charging a cold iron source having a specific surface area of 0.5 to 11.0 m ² / ton in the converter. Next, there is proposed a refining method having a fourth step in which quick lime is charged into a converter, oxygen gas is blown into the converter, decarburization and refining are performed simultaneously with decarburization refining, and further, tapping is performed. That is, a technique has been proposed in which the cold iron source is charged twice into the converter with one converter refining.

JP 2000-328123 A JP 2001-192720 A JP 2013-189714 A WO 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 and dephosphorization treatment → drainage process → decarburization refining in which the double slag method is applied to the converter steelmaking method disclosed in Patent Documents 1 and 2, the desiliconization / dephosphorization in the first half is performed. The problem is that it is difficult to reduce the phosphorus in the molten steel in the latter half of the decarburization refining because the phosphorus concentration of the hot metal does not drop sufficiently at the stage of treatment and the waste cannot be completely discharged. There is.

  On the other hand, in the case of the desiliconization treatment → the waste → the dephosphorization treatment that applies the double slag method to the hot metal pretreatment disclosed in Patent Documents 3 to 6, the phosphorus concentration of the hot metal after the dephosphorization treatment is reduced. In addition, since decarburization and refining are performed in another converter, it is possible to reduce the phosphorous of the molten steel to be produced, but there is a problem that productivity is low because two converters are used. is there.

  According to the technology disclosed in Patent Document 7 in which a cold iron source is charged twice into a converter, a low basicity, high viscosity slag generated by desiliconization in the furnace at the time of the second cold iron source charging. , There is a problem that the charged cold iron source is coated with slag in the furnace, and the melting efficiency during refining is reduced.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to use a single converter, oxygen-blown hot metal charged in the converter, and produce molten steel from the hot metal. In the converter steelmaking method, by providing a converter steelmaking method capable of lowering the phosphorus concentration of the molten steel to be melted and increasing the productivity of the converter and the melting efficiency of the cold iron source. is there.

The gist of the present invention for solving the above problems is as follows.
[1] A converter steelmaking method for refining hot metal in one converter to produce molten steel from the hot metal, wherein a 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 supplying oxygen gas to the hot metal from the top blow lance while stirring the hot metal in the converter with the bottom blown gas to desiliconize the hot metal in the converter; and 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 into the converter, and A fourth step in which oxygen gas is supplied to the hot metal from the upper blowing lance while the hot metal in the inside is stirred by the bottom blow gas to remove the hot metal remaining in the converter, and the fourth step is performed by tilting the converter again. A fifth step of discharging at least a part of the slag generated in the step from the converter, returning the converter to the upright position, and placing C in the converter. The sixth method of supplying an O-based solvent and supplying oxygen gas to the hot metal from the top blowing lance while stirring the hot metal in the converter with the bottom blown gas to decarburize and refine the hot metal remaining in the converter. The first step of the next charge is performed in a state where the slag generated in the sixth step remains in the converter, and the slag generated in the sixth step is desiliconized in the next charge. A converter steelmaking method that is reused 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 in the same slag holding container.
[3] Before the hot metal is charged into the converter in the first step, after the third step, and in 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 the above [1] or [2].
[4] Before the hot metal is charged into the converter in the first step, a cold iron source is charged into the converter, and after the third step and / or after the fifth step, the cold iron source is charged into the converter. The converter steelmaking method according to the above [1] or [2], wherein a cold iron source is charged.
[5] Before the hot metal is charged into the converter in the first step, after the third step, and after the fifth step, the charging amount of the cold iron source in each period The converter steelmaking method according to the above [3] or [4], wherein the content is set to 10% by mass or less of the total iron source charged into the converter.

  According to the present invention, in a converter steelmaking method for producing molten steel from hot metal in one converter, desiliconization, dephosphorization, and decarburization refining are separately performed, and desiliconization and dephosphorization are performed. After the treatment, each waste is discharged and slag is formed in the furnace three times, so the discharge of the phosphorus contained in the hot metal to the outside of the furnace is promoted, and the phosphorus concentration of the molten steel after the decarburization refining is stabilized. Lowering is realized. In addition, the decarburized slag generated in the decarburization refining is left in the furnace and reused as a CaO source for the desiliconization of the next charge, so the slag discharged outside the system is desiliconized slag and dephosphorized slag. Not only the amount of slag discharged is reduced, but also the calorific value and iron content of the decarburized slag of the previous charge can be recovered in the desiliconization process of the next charge, and the recovered calorific value Dissolution is promoted, and the recovered iron content improves the iron yield. Furthermore, in the present invention, since the molten metal in the furnace is refined without discharging it from the furnace using one converter, a decrease in the productivity of the converter is suppressed.

  Further, in the present invention, the cold iron source can be added in a plurality of portions, and the dissolution of the cold iron source is promoted, which contributes to reducing the amount of carbon dioxide gas generated.

It is a schematic sectional view of a converter used when performing a converter steelmaking method concerning the present invention. It is a schematic diagram showing a converter steelmaking method concerning the present invention in order of a process.

  Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a schematic sectional view of a converter used when carrying out the converter steelmaking method according to the present invention, and FIG. 2 is a schematic diagram showing the converter steelmaking method according to the present invention in the order of steps. FIG. 1 is a view showing the silicon removal treatment in the second step of FIG.

  In the converter steelmaking method according to the present invention, a converter 1 capable of being blown up and down as shown in FIG. 1 is used. The upper blowing is performed by supplying an oxygen-containing gas as a source of oxygen toward the hot metal 5 from the tip of the upper blowing lance 2 through an upper blowing lance 2 that can move up and down inside the converter 1. As the oxygen-containing gas, oxygen gas, oxygen-enriched air, air, and 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-blown gas 9 may be a gas containing oxygen gas or only an inert gas such as argon gas or nitrogen gas, and is blown into the hot metal to enhance the stirring of the hot metal 5 to promote melting of the cold iron source. What is necessary is just to have the function to perform.

  In the present invention, one converter 1 is used for refining the hot metal 5, desiliconization processing and dephosphorization processing of the hot metal pretreatment are performed, and waste is discharged after the desiliconization processing and after the dephosphorization processing. Is performed, and 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 a converter 1 via a scrap chute 10 as shown in FIG. In the present invention, it is essential that the slag (referred to as “decarburized slag”) generated in the decharging and refining of the pre-charge performed in the converter 1 remain in the converter, and thus the decarburized slag remains. The cold iron source 7 will be charged inside the converter 1. FIG. 2- (A) shows the state of the first charge (operation of the decharging slag of the previous charge is performed) after the start of operation such as after periodic repair. Absent state).

  Note that charging of the cold iron source 7 into the converter 1 is not an essential condition for carrying out the present invention, but in order to reduce the amount of carbon dioxide gas generated in the steelmaking process, the converter 1 of the cold iron source 7 is required. It is preferable to carry out charging.

  Next, as shown in FIG. 2 (B), hot metal 5 (hereinafter, referred to as “blast furnace hot metal 5”) that has been tapped from a blast furnace via a charging pan 11 and desulfurized as necessary, ") (First step).

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

In the present invention, the decarburization slag generated in the decarburization refining before charge made in this converter 1 is allowed to remain in the converter in a CaO source, SiO ₂ produced by desiliconization reactions in the furnace The slag 6 is generated by reacting with the pre-charged decarburized slag. Since the slag 6 generated in the desiliconization treatment is also referred to as “desiliconization slag”, the slag 6 generated in the desiliconization treatment is hereinafter referred to as “desiliconization slag 6”.

In the desiliconization treatment, the basicity ([% by mass CaO] / [% by mass SiO ₂ ]) of the desiliconized slag 6 (hereinafter, sometimes referred to simply as “basicity”) is 0.5 or more, preferably. Is maintained at 0.8 or more. 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 pre-charged decarburized slag during the desiliconization treatment. The phosphor of 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 “rephosphorization”), and the phosphorus concentration of the hot metal 14 after the desiliconization treatment is higher than that before the desiliconization treatment. This is because it can be high. Phosphorus reversion does not occur as the basicity of the desiliconized slag 6 increases. Therefore, the basicity of the desiliconized slag 6 is preferably set to 0.8 or more.

The decarbonized slag of the pre-charge remaining in the furnace is diluted by SiO ₂ generated by the de-siliconization treatment, and the basicity of the de-siliconized slag 6 generated in the furnace is gradually reduced. Since the basicity of the decarburized slag is as high as 2.5 to 5.0, the basicity of the desiliconized slag 6 generated in the furnace is usually maintained at 0.5 or more.

  However, in the case of the first charge after the start of operation such as after regular repair, the decarburized slag of the previous charge does not remain in the furnace, and therefore, the basicity of the desiliconized slag 6 is adjusted to 0.5 or more. It is necessary. In addition, there may be a case where the decarburized slag of the pre-charge is left or a case where the basicity of the desiliconized slag 6 must be adjusted to 0.5 or more.

  As described above, when the basicity of the desiliconization slag 6 is adjusted to 0.5 or more, a CaO-based solvent is added to the converter 1 before and / or during the desiliconization. The addition amount of the CaO-based solvent does not need to be excessively large, and the upper limit of the basicity of the desiliconized slag 6 may be set to about 1.5.

  As the CaO-based solvent in the desiliconization treatment, quicklime, dolomite, calcium carbonate and the like can be used. Further, the decarburized slag may be cooled and solidified, and the solidified decarburized slag may be crushed, or the lumped or powdered decarburized slag may be used as the CaO-based medium solvent without crushing.

  As an oxygen source for the desiliconization treatment, only the oxygen gas 8 from the upper 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 the target basicity during the desiliconization treatment performed in a short time, it is effective to use iron oxide having a function of promoting slagging of the CaO-based solvent. However, in the present invention, since the decarburized slag in the molten state is used as the CaO-based solvent, even if the desiliconization treatment is performed using only the oxygen gas 8, the desiliconized slag having the target basicity sufficient can be obtained. 6 can be formed. Further, since the converter 1 capable of strong stirring is used as a refining vessel, the desiliconized slag 6 having a sufficiently basic basicity can be formed even when only the oxygen gas 8 is used.

After the desiliconization treatment, as shown in FIG. 2D, the converter 1 is tilted to provide a waste disposal step, and the desiliconization slag 6 containing a large amount of SiO ₂ generated in the desiliconization treatment is provided. Is discharged from the furnace opening of the converter 1 to a slag holding vessel (not shown) (third step).

In order to discharge the SiO ₂ generated by the desiliconization process to the outside of the furnace as much as possible, a waste rate (a waste rate (mass%) = (mass of discharged slag) × 100 / (mass slag mass at the end of the desiliconization process)) ) Is preferably 50% by mass or more. In order to secure a waste 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 more. Is preferred.

  After the desiliconization slag 6 is discharged, the converter 1 is returned to the upright position with the furnace port facing upward, and the desiliconized hot metal 14 remaining in the converter (hereinafter referred to as “siliconized hot metal 14”). 2), a CaO-based solvent and an oxygen source are supplied, and as shown in FIG. 2- (E), the desiliconized hot metal 14 is subjected to a dephosphorization treatment (fourth step). The slag generated in the dephosphorization treatment is also called “dephosphorization slag”, and hence the slag 12 generated in the dephosphorization treatment will be 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. Since higher basicity of dephosphorization slag 12 phosphorus oxides (3CaO · P ₂ O ₅ becomes) absorbing power becomes high dephosphorization reaction is accelerated, in order to promote the dephosphorization reaction, dephosphorization slag 12 Is controlled to 1.5 or more. On the other hand, if the basicity of the dephosphorized slag 12 exceeds 3.5, the slagging property of the dephosphorized slag 12 deteriorates, and the dephosphorization reaction becomes slow. Therefore, the basicity of the dephosphorized slag 12 is reduced to 3.5 or less. Control.

  Examples of the CaO-based solvent used in the dephosphorization treatment include quicklime, dolomite, and calcium carbonate. However, not limited to these, those containing 50% by mass or more of CaO and optionally containing other components such as fluorine and alumina can also be used as a CaO-based solvent in the dephosphorization treatment. . As a method of adding the CaO-based solvent, the granular and bulky materials can be introduced from a hopper on a furnace, and the powdery one can be introduced through an upper blowing lance 2 or the like.

  The oxygen source used in this dephosphorization treatment step is mainly oxygen gas 8 from the upper blowing lance 2 as in the desiliconization treatment, but iron oxide may be partially used.

Phosphorus contained in the desiliconized hot metal 14 is oxidized to oxygen in the supplied oxygen source to form phosphor oxide (P ₂ O ₅ ), and this phosphor oxide is formed by slagging of a CaO-based solvent, and the dephosphorization slag 12 which functions as a refining agent incorporated as a compound of 3CaO · P ₂ O ₅ becomes stable form, dephosphorization reaction of de珪溶pig iron 14 progresses. When the dephosphorization reaction has progressed and the phosphorus concentration of the desiliconized hot metal 14 has decreased to a predetermined value, the dephosphorization treatment is terminated.

  In order to stably reduce the phosphorus concentration of the molten steel produced by the decarburization refining in the subsequent step, the phosphorus concentration of the hot metal 15 after the dephosphorization treatment (hereinafter, referred to as “dephosphorized hot metal 15”) is set to 0.1. It is preferable to perform the dephosphorization treatment until the amount becomes 040% by mass or less.

After this dephosphorization, as shown in FIG. 2-(F), and the converter 1 is again tilted, provided Haikasu process occurred in dephosphorization, containing 3CaO · P ₂ O ₅ At least a part of the dephosphorized slag 12 is discharged from the furnace port of the converter 1 to a slag holding vessel (not shown) (fifth step).

  At this time, it is preferable that the desiliconized slag 6 is discharged in the third step, and the dephosphorized slag 12 is discharged to 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 physical distribution 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 treatment as much as possible outside the furnace, a waste rate (a waste rate (mass%) = (mass of discharged slag) × 100 / (furnace at the end of the dephosphorization treatment) (Internal slag mass) is preferably 50% by mass or more.

  After the dephosphorization slag 12 has been discharged, the converter 1 is returned to the upright position with the furnace port facing upward, and a CaO-based solvent and an oxygen source are added to the dephosphorized hot metal 15 remaining in the converter after the dephosphorization treatment. To perform decarburization refining on the dephosphorized hot metal 15 as shown in FIG. 2- (G) (sixth step).

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

  As the CaO-based solvent used in the decarburization refining, quicklime, dolomite, calcium carbonate and the like can be used. However, not limited to these, those containing 50% by mass or more of CaO and optionally containing other components such as fluorine and alumina can also be used as a CaO-based solvent in decarburization refining. . As a method of adding the CaO-based solvent, the granular and bulky materials can be introduced from a hopper on a furnace, and the powdery one can be introduced through an upper blowing lance 2 or the like. The oxygen source used in the decarburization refining is mainly oxygen gas 8 from the upper blowing lance 2.

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

  After tapping the molten steel 16, 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 molten iron 5 is charged into the converter 1, and the desiliconization treatment of the next charge is started. The decarburized slag 13 remaining in the furnace is effectively used as a CaO source in the desiliconization treatment of the next charge. When a part of the decarburized slag 13 is subjected to the waste treatment, the treatment time is lengthened by the waste time, and the productivity of the converter 1 is reduced. Preferably, no slag treatment is performed. 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 insert as many cold iron sources 7 as possible in order to improve productivity and reduce carbon dioxide gas emissions. From this viewpoint, before charging the hot metal into the converter in the first step, after the third step, in at least one of the periods after the fifth step, the cold iron source is introduced into the converter. It is preferred to charge. In particular, as described above, before the molten iron 5 in the blast furnace is charged into the converter 1 in the first step, the cold iron source 7 is charged into the converter 1 and further, by the desiliconization treatment (second step). 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 treatment (fourth step), the cooling furnace is cooled 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 unmelting of the cold iron source. . Even when the total charge amount of the cold iron source 7 is the same, the dissolution of 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 in the charge and the mass of the cold iron source.

  When increasing the amount of the cold iron source 7 to be charged, 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 treatment in the blast furnace cast floor.

  As described above, according to the present invention, in a converter steelmaking method for producing molten steel 16 from blast furnace molten iron 5 in one converter 1, desiliconization, dephosphorization, and decarburization refining are separately performed. After the desiliconization treatment and the dephosphorization treatment, the slag is formed in the furnace three times (triple slag method) after the desiliconization treatment and the dephosphorization treatment, so that the phosphorus contained in the blast furnace hot metal 5 is discharged outside the furnace. The discharge is promoted, and it becomes possible to stably realize the low phosphorus reduction of the molten steel 16 after the decarburization refining, which is a problem when the double slag method is applied to the converter steelmaking method. In addition, the decarburized slag 13 generated by the decarburization refining is left in the furnace and reused as a CaO source for the desiliconization of the next charge. Only the phosphorus slag 12 is provided, and not only the amount of slag discharged is reduced, but also the calorific value and iron content of the decarburized slag 13 of the previous charge can be recovered in the desiliconization process of the next charge. The melting of the cold iron source 7 is promoted, and the recovered iron content improves the iron yield. Furthermore, in the present invention, since the molten metal in the furnace is refined without discharging the molten metal from the furnace using one converter 1, a decrease in 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 (Example 1 of the present invention). For comparison, the waste is treated only once after the dephosphorization treatment. After the dephosphorization treatment, the dephosphorized hot metal is discharged and charged into another converter for decarburization refining, or A test operation without recycling coal slag (Comparative Examples 1 to 3) was also performed.

  Table 1 shows the supply conditions of top-blown oxygen gas and bottom-blown nitrogen gas for stirring in desiliconization treatment, dephosphorization treatment, and decarburization refining using a converter in Example 1 of the present invention and Comparative Examples 1 to 3, Shows blowing time and mass of hot metal to be refined.

  Table 2 shows the test conditions of Inventive Example 1 and Comparative Examples 1 to 3. As shown in Table 2, in Inventive Example 1 and Comparative Examples 1 to 3, the test was performed without charging a cold iron source.

  Comparative Example 1 is a double slag method of desiliconization and dephosphorization → waste and decarburization refining, and Comparative Example 2 is desiliconization → waste → dephosphorization → hot water → recharge to another converter → The double slag method of decarburization refining, Comparative Example 3 is a triple slag method of desiliconization treatment → wastewater → dephosphorization treatment → wastewater → decarburization refining, but is a condition in which decarburization slag is not reused. . The present invention example 1 is a triple slag method of desiliconization treatment → wastewater → dephosphorization treatment → wastewater → decarburization refining, and the decarburized slag is left in the converter without being discharged, and The charged hot metal was charged, and the remaining decarburized slag was reused in the desiliconization treatment of the next charge. In Example 1 of the present invention, desiliconized slag and dephosphorized slag were discharged into the same slag holding container.

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

  In Comparative Example 1, only the waste after the desiliconization and dephosphorization treatment was performed, and therefore, the total treatment time was short. However, since the phosphorus concentration in the hot metal at the time of the waste after the desiliconization and dephosphorization treatment was high (0.055% by mass), and the waste ratio was 60% by mass, it remained in the furnace during the decarburization refining. The phosphorus content of the molten steel after the decarburization refining was high (0.012% by mass).

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

  Comparative Example 3 is a triple slag method, and has a longer total processing time than Comparative Example 1, but has a shorter total processing time than Comparative Example 2 in which tapping and recharging are performed. Further, the dephosphorized hot metal is reduced in phosphorous, and although the removal rate of dephosphorized slag is lower than that of Comparative Example 2 in which dephosphorized slag is almost completely removed outside the furnace, the molten steel after decarburization refining has a lower removal rate. Thickening had been realized. However, since slag was not reused, the quicklime basic unit was as high as 28 kg / molten steel-t.

  In contrast to Comparative Examples 1 to 3, in Inventive Example 1, the metallurgical properties are the same as in Comparative Example 3, and the decarburized slag is reused for the desiliconization treatment, so the quicklime basic unit is 25 kg / molten steel-t. And was low. Further, since the decarburized slag was not discharged, the total processing time was shorter than that in Comparative Example 3.

  Next, tests were performed to compare the melting state of the cold iron source by changing the charging time and the charging amount of the cold iron source into the converter (Examples 2 to 8 of the present invention).

  The refining method was the same as that of Example 1 of the present invention, and was a triple slag method of desiliconization → waste → dephosphorization → waste → decarburization refining, and the decarburized slag was reused for desiliconization. In Examples 2 to 8, the amount of the cold iron source charged was constant at 25% by mass of the total iron source charged into the converter. That is, the total iron source was set to 300 tons, and the cold iron source of 75 tons per charge was charged into the blast furnace hot metal of 225 tons per charge. Of the 75 tons of cold iron source, the 45 tons of 60 mass% of the cold iron source used was obtained by cutting heavy waste having a thickness of 10 mm or more. Lightweight debris less than 10 mm was used. Table 4 shows the 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 corresponding to a total of 25% by mass of the total iron source, in Example 2 of the present invention, 5% by mass (light waste = 15 tons) and 15% by mass were removed before charging the blast furnace hot metal. A 10% by mass (weight waste = 15 tons) cold iron source after the silicon slag was discharged and a 10% by weight (weight waste = 30 tons) cold iron source after the dephosphorization slag were disposed in the converter. Entered.

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

  In Inventive Example 5, 10% by mass (light waste = 15 tons, heavy waste = 15 tons) before charging the blast furnace molten iron, and 15% by mass (light waste = 15 tons, heavy waste = 30 tons) of cold iron source was charged into the converter, and in Example 6 of the present invention, 5% by mass (weight waste = 15 tons) before charging the molten iron in the blast furnace, and 15% by mass after discharging the desiliconized slag. (Lightweight debris = 15 tons, heavy debris = 30 tons), and a 5 mass% (lightweight debris = 15 tons) cold iron source was charged into the converter after the dephosphorization slag was discharged.

  In Example 7 of the present invention, 5% by mass (weight debris = 15 tons) before charging the blast furnace molten iron, 5% by mass (light weight debris = 15 tons) after the desiliconized slag was discharged, and 15% by weight after the dephosphorized slag was discharged. A cold iron source of mass% (light waste = 15 tons, heavy waste = 30 tons) was charged into the converter, and in Example 8 of the present invention, 15% by mass (light waste = 15 tons) before charging of blast furnace hot metal. , Heavy waste = 30 tons), 5 mass% (light waste = 15 tons) after desiliconization slag discharge, and 5 mass% (weight waste = 15 tons) cold iron source after dephosphorization slag discharge. Was charged inside.

  In Example 3 of the present invention, when the converter was tilted at the time of the waste after the desiliconization treatment and at the time of the waste after the dephosphorization treatment, an undissolved cold iron source was confirmed at the furnace bottom. After tapping after decarburization refining, undissolved cold iron sources were found in the decarburized slag remaining in the furnace.

  In Inventive Examples 4 and 5, similarly to Inventive Example 3, at the time of the waste after the desiliconization treatment and at the time of the waste after the dephosphorization treatment, a part of the undissolved cold iron source was placed at the bottom of the furnace. Was observed. After tapping after decarburization refining, a small amount of unmelted cold iron source was observed in the slag remaining in the furnace.

  In Examples 6 to 8 of the present invention, although the amount of the cold iron source remaining was smaller than that of Examples 4 and 5 of the present invention, the amount of residual iron remained in the furnace at the bottom of the furnace or after tapping after decarburization refining. A slight undissolved source of cold iron was found in the slag.

  On the other hand, in Example 2 of the present invention, the decarburized slag remaining in the furnace after the desiliconization treatment, at the waste after the dephosphorization treatment, and after tapping after the decarburization refining was not added. No source of cold iron for dissolution 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 unmelted cold iron source adheres to the furnace bottom, and the cold iron source is mixed with slag. It has been found that undissolution of the source is reduced. In addition, even when the cold iron source is dispersed, in each step, that is, before the hot metal charging, after the waste after the desiliconization treatment, and after the waste after the dephosphorization treatment, the amount exceeding 10% by mass of the total iron source. 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 due to mixing with the slag. Therefore, the amount of the cold iron source charged into the converter before charging the hot metal, after the waste after the desiliconization treatment, and after the waste 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. The metallurgical properties of the desiliconization reaction, dephosphorization reaction and decarburization reaction in Inventive Examples 2 to 8 in which the dissolution behaviors of the cold iron source were compared were the same as in Inventive Example 1.

Reference Signs List 1 converter 2 top blowing lance 3 bottom blowing tuyere 4 tap hole 5 blast furnace hot metal 6 desiliconized slag 7 cold iron source 8 oxygen gas 9 bottom blowing gas 10 scrap chute 11 charging pan 12 dephosphorized slag 13 decarburized slag 14 desorption Hot metal 15 Dephosphorized hot metal 16 Molten steel

Claims (4)

A converter steelmaking method for refining hot metal in one converter and producing molten steel from the hot metal,
A first step of charging hot metal into the converter;
A CaO-based solvent is supplied into the converter, and while the hot metal in the converter is stirred by the bottom blown gas, oxygen gas is supplied to the hot metal from the upper blow lance to desiliconize the hot metal in the converter. Two steps,
A third step of inclining the converter and discharging at least a part of the slag generated in the second step from the converter;
Return the converter to the upright position, supply the 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 blown gas. A fourth step of dephosphorizing the hot metal remaining in the
A fifth step of tilting the converter again and discharging at least a part of the slag generated in the fourth step from the converter;
Return the converter to the upright position, supply the 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 blown gas. A sixth step of decarburizing and refining the hot metal remaining in the
Consisting of
The slag discharged in the third step and the slag discharged in the fifth step are discharged into the same slag holding container,
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 in the desiliconization treatment of the next charge. The converter steelmaking method to be used. Loading the cold iron source into the converter before charging the hot metal into the converter in the first step, after the third step, and in at least one of the periods after the fifth step; The converter steelmaking method according to claim 1 . Before the hot metal 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, the cold iron source is charged into the converter. The converter steelmaking method according to claim 1, wherein a source is charged. Before the hot metal is charged into the converter in the first step, after the third step, and after the fifth step, the charging amount of the cold iron source in each period is charged into the converter in any period. The converter steelmaking method according to claim 2 or 3 , wherein the total iron source is set to 10% by mass or less.

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