BR112013020045B1 - desalination and dephosphorization method of cast iron - Google Patents

Abstract

patent abstract: "method of desalination and dephosphorylation of molten pig iron". The present invention relates to a method of desiliconization and dephosphorylation of a molten pig iron includes an oxygen gas blowing process of blowing an oxygen gas from an oven top towards a surface of the molten pig iron; a process of adding recycled slag providing at least one of a decarburization slag and a secondary refining slag facing the surface of cast iron as a recycled slag; and a process for adding quicklime fine powder to providing a quicklime fine powder having a maximum particle size of 500 µm or less together with the oxygen gas blowing to the surface of the cast iron in which The process of adding quicklime fine powder begins at a starting time when a concentration of silicon in the molten pig iron is reduced to 0 mass% or more and 0.15 mass% or less. 1/1

Description

(54) Title: METHOD OF DESILICONIZATION AND DEPHOSPHORATION OF CAST IRON (51) Int.CI .: C21C 1/02; C21C 1/04 (30) Unionist Priority: 10/02/2011 JP 2011-027338, 28/02/2011 JP 2011-041220 (73) Holder (s): NIPPON STEEL & SUMITOMO METAL CORPORATION (72) Inventor (s) : SUSUMU MUKAWA; HIROSHI MATSUMOTO; TSUYOSHI NAKAJIMA; KAZUNORI FUKIAGE; TOMOAKI TASAKI (85) National Phase Start Date: 08/06/2013

1/46

Descriptive Report of the Invention Patent for METHOD OF CAST IRON DESYLICONIZATION AND DEPHOSPHORATION.

Technical Field [001] The present invention relates to a method of desiliconisation and dephosphorization of a molten pig iron, and particularly refers to a method of desiliconisation and dephosphorization suitable for molten pig iron with a high concentration of Si (eg example, a Si content: 0.4% by mass or greater).

[002] The priority is claimed in Japanese Patent Application No. 2011-27338, filed on February 10, 2011, and Japanese Patent Application No. 2011-41220, filed on February 28, 2011, and the content of which is incorporated here by references.

Background Art [003] When the environment for using steel products becomes more severe, the requirements for a reduction of impurity elements in steel such as phosphorus and sulfur become more severe.

[004] In order to meet these requirements, a technique for removing silicon, sulfur, and phosphorus from pig iron, extracted from an explosion furnace, in advance in a process before a decarburization refinement; and carrying out a converter blow to obtain the steel, that is, a so-called pre-treatment technique for cast pig iron was developed. This pre-treatment of cast iron was generally carried out using a torpedo car in the past. However, recently, cases where the pretreatment of cast pig iron is carried out using a converter have been increased.

[005] In particular, recently, the demand for low phosphorus steel has been increased. In addition, a reduction in the amount of slag generation was also required due to problems relating it and a rationalization in the production cost of the slag.

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2/46 steel and a slag treatment.

[006] In general, in a molten pig iron dephosphorization reaction, in order to oxidize the phosphorus in the pig iron and remove the pig iron phosphorus into a slag, it is necessary that a source of oxygen and oxygen ions be applied to phosphorus in cast pig iron; and ions of stably produced in the slag. In this case, the oxygen ions are supplied to an interface between the molten pig iron and the slag by a basic oxide such as CaO forming a molten slag.

[007] Since the slag contains CaO, it is preferable that the slags, produced in processes other than the dephosphorization process, are recycled by a dephosphoration reaction, from the point of view of reducing the amount of slag generation.

[008] However, the slags produced in a decarburization process or a secondary refining process or similar (here below, referred to as a decarburization slag and a secondary refining slag, respectively) contain high concentrations of SiO2 and ALO3 other than CaO . Therefore, when these slags are recycled in the dephosphorization process (a melting process of molten pig iron), there is a problem with the fact that the amount of slag is increased; and the risk of overflow where the slag overflows from an oven is increased. Among the components, Al2O3 is known as a chemical component of significant promotion of a slag foam (for example, it refers to Non-Patent Document 1). In addition, as a countermeasure for overflowing, a method of increasing oven capacity is not preferable from the point of view of an installation cost.

[009] In addition, cast iron contains impurities other than phosphorus. In particular, recently, a use of a mineral ore

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3/46 iron having a high Si content was increased from the point of view of reducing production costs.

[0010] From the point of view of optimizing the treatment of pig iron, it is preferable that silicon and phosphorus contained in pig iron are removed in the same process. As a technique of efficiently preparing a low phosphorus steel, the present inventors describe a technique for removing silicon contained in pig iron in the same process as a phosphorus removal process (Patent Document 1).

[0011] When the silicon and phosphorus contained in the pig iron are removed in the same process, the amount of slag is increased due to the SiO2 produced by a desiliconization reaction. Therefore, there is a problem with the fact that overflow is likely to occur. In order to avoid this problem, the present inventors describe a technique in which an oxygen gas, blowing from a top blowing spear, is used as a carrier gas to blow a fine powder of quicklime into the pig iron (Document of Patent 2).

[0012] However, when molten pig iron having a higher Si content (for example, 0.4% by mass or greater) than that of the related technique is treated, the amount of slag is increased due to the SiO2 produced by the reaction desiliconization. Therefore, when the recycled slag described above (for example, decarburization slag or secondary refining slag) is used as a source of supply of oxygen ions used for a dephosphoration and desiliconisation reaction, particularly a foam problem of slag becomes remarkable.

[0013] The secondary refining slag described in this specification includes a shell slag produced during secondary refining; and a funnel slag used to prevent oxidation

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4/46 of air from a steel cast in a funnel during continuous casting and for maintaining the temperature.

Prior Art Document

Patent Document [0014] Patent Document 1 Japanese Unexamined Patent Application, First Publication No. H2-47212 [0015] Patent Document 2 Japanese Unexamined Patent Application, First Publication No. 2002-256320 [0016] Patent 3 Japanese Unexamined Patent Application, First Publication No. H11-172315 Non-Patent Document [0017] Non-Patent Document 1 High Temperature Interfacial Transport Phenomena in Pyrometallurgical Processes, page 57, by Ryouji TSUJINO and Eiji AIDA

Description of the Invention

Problem to be solved by the invention [0018] An objective of the present invention is to solve the problems described above and to provide a method for desiliconisation and dephosphorization of molten pig iron in which a recycled slag generated in a molten steel stage is used as a source of supply of oxygen ions, which are used for the dephosphoration and desiliconization reaction of cast iron having a higher Si content (eg 0.4% by mass or greater) than that of the related technique, to suppress foam slag while reducing the amount of total slag discharge on the molten steel stage; and as a result, overflowing can be efficiently prevented without increasing oven capacity.

Means for Solving Problems (1) In accordance with an aspect of the present invention, a method of desiliconisation and dephosphorization of pig iron is provided

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5/46 molten including: a process of blowing oxygen gas blowing oxygen gas from a furnace top towards a surface of the molten pig iron; a process for adding recycled slag to supply at least one of a decarburization slag and a secondary refining slag to the cast iron surface as a recycled slag; and a process for adding fine quicklime powder providing a fine quicklime powder having a maximum particle size of 500 mm or less, together with the oxygen gas blowing on the surface of the pig iron, in which the The process of adding fine quicklime powder starts at a starting time in which a concentration of silicon in the molten pig iron is reduced to 0% by weight or more and 0.15% by weight or less.

(2) In the molten pig iron desiliconisation and dephosphorization method according to (1), the silicon concentration in the molten pig iron at the time of departure may be 0% by weight or more and 0.08% by weight or less .

(3) In the molten pig iron desiliconization and dephosphorization method according to (1) or (2), in the process of adding recycled slag, when the concentration of silicon in the pig iron at the time of the start of the process of adding recycled slag is less than 0.6% by mass, only secondary refining slag or both decarburization slag and secondary refining slag can be supplied to cast pig iron, and when the concentration of silicon in cast pig iron at the time of starting the process of adding recycled slag is greater than or equal to 0.6% by mass, only decarburization slag can be supplied for cast pig iron.

(4) In the molten pig iron desiliconization and dephosphorization method according to any one of (1) to (3), in the process of adding recycled slag, when the secondary refining slag

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6/46 is supplied to the surface of the pig iron, a quantity of secondary refining slag per 1 ton of the pig iron can be in a range between 0.1 kg and 16 kg.

(5) The molten pig iron desiliconization and dephosphorization method according to any one of (1) to (4) may also include a process for adding a solid oxygen source by providing a solid oxygen source to the iron surface. cast pig iron.

(6) The molten pig iron desiliconisation and dephosphorization method according to any one of (1) to (5) may also include a process for adding a massive CaO source to supply a massive CaO source, which is derived of an ore having an average particle size of 5 mm or larger, on the surface of the pig iron, where in the process of adding a massive CaO source, an amount of the massive CaO source per 1 ton of the pig iron can be limited to less than or equal to 7.5 kg.

(7) In the molten pig iron desiliconization and dephosphorization method according to any one of (1) to (6), a total amount of MnO in the recycled slag can be greater than 0% by weight and less than or equal to to 25% by mass.

(8) The molten pig iron desiliconisation and dephosphorization method according to any one of (1) to (7) may also include a gas blowing process for molten pig iron and molten pig iron agitation with a agitation force ε within a range between 1.2 kW / t and 10 kW / t which is defined according to the following Formula 1.

0.0062 xQ _f * T

(Formula 1) where ε: a base blowing agitation force (W / t) applied

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7/46 to cast pig iron

Qg: an amount of the base blowing gas (NL / minute; including a gas cracked from a solid material (for example, a fine limestone powder))

T: a temperature of molten pig iron (K) at the start of a baseline

Tg: a temperature (K) of the base blowing gas before blowing

H0: a depth of sofro (distance from a liquid surface of the molten pig iron to a tip end of a base blowing mesquite; (m))

Wm: a weight of the molten pig iron (including a scrap load; (t)) (9) In the method of desiliconisation and dephosphorization of the molten pig iron according to (8), in the stirring process, a fine limestone powder can be supplied for the pig iron together with the blowing gas for the pig iron.

Effects of the Invention [0019] In the molten pig iron desiliconization and dephosphorization method according to (1), a fine powder of quicklime is blown onto the surface of the pig iron after the concentration of silicon in the pig iron is reduced to less than or equal to 0.15% by weight. As a result, even when the silicon concentration in the pig iron is high, the desiliconisation and dephosphorization of the pig iron can be efficiently carried out in the same process. In addition, the molten pig iron desiliconization and dephosphorization method according to (1) includes two processes for adding recycled slag to add at least one of the decarburization slag and the refining slag secondary to the pig iron. ; and the process of adding fine powder to

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8/46 quicklime with the addition of fine quicklime powder to cast iron. Therefore, the recycled slag generated in the molten steel stage is used to efficiently prevent overflow without increasing the capacity of the furnace while reducing the amount of total discharge of the slag in the molten steel stage.

[0020] When the concentration of Si in the pig iron is high; and only a fine top blowing lime powder is used, the cost required to supply a source of CaO is significantly increased. However, when a combination of recycled slag and fine lime powder is used as the source of CaO, the cost required to supply the source of CaO can be reduced. [0021] In addition, in the melting pig iron desiliconization and dephosphorization method according to (7), Mn contained in the secondary refining slag and Mn contained in the decarburization slag are transferred to the pig iron; and as a result, a concentration of Mn in the molten pig iron after desiliconization and dephosphorization can be improved. Therefore, when steel products containing Mn according to the production specification are produced, the amount of use of an expensive Mn ore or Mn alloy can be reduced in a post-process.

Brief Description of the Drawings [0022] FIG. 1 is a schematic diagram (vertical cross-section) illustrating a dephosphor furnace that is desirably used in an embodiment of the present invention.

[0023] FIG. 2 is a diagram illustrating an example of a basic process when a method of desiliconisation and dephosphorization of cast iron according to a modality of the present invention is applied to a steel fabrication.

[0024] FIG. 3 is a diagram illustrating an example of a process graph according to one embodiment of the present invention. Petition 870180045283, of 28/05/2018, pg. 13/60

9/46 tion.

[0025] FIG. 4 is a schematic diagram (vertical cross-section) illustrating a decarburization furnace from which a decarburization slag is discharged.

[0026] FIG. 5 is a diagram illustrating a relationship between a quantity of slag discharge and a concentration of silicon in the pig iron [% Si].

[0027] FIG. 6 is a diagram illustrating an example of a particle size distribution of a fine powder of quicklime used in an embodiment of the present invention.

Modalities of the Invention [0028] In the following, preferred embodiments of the present invention will be described. In particular, one embodiment of the present invention relates to a desiliconisation and dephosphorization method suitable for a cast iron with a high concentration of Si (for example, Si content: within a range between 0.45% by mass and 0.65% by mass). Next,% represents mass% unless otherwise specified.

[0029] First, massive auxiliary materials (a particle size: 5.0 mm or larger) are added from a feed hopper 8 (a top hopper) to a cast pig iron P in a dephosphor furnace 1 (an oven cast iron dephosphorization) illustrated in FIG. 1 (a process for adding auxiliary material). In the modality, as such auxiliary materials, recycled slag (post-process slag) such as decarburization slag and secondary refining slag are used, and a solid oxygen source such as iron ore and dolomite can also be used. . As illustrated in FIG. 2, the recycled slag described here refers to slag (for example, secondary refining slag such as decarburization slag, shell slag, and

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10/46 a funnel slag) which are used or produced in processes (for example, a decolorization blow, a secondary refining, and a continuous casting) subsequent to a desiliconisation and dephosphorization treatment (corresponding to the dephosphoration oven 1). Among such recycled slags, the decarburization slag to be loaded into the feed hopper 8 is obtained by unloading a slag from a decarburization furnace; cooling and crushing this slag; removing a base metal from the crushed slag by a magnetic separation; and crushing the slag to a size preferably less than 50 mm. In addition, the secondary refining slag to be loaded into the feed hopper 8 is obtained by unloading a slag, remaining in a shell or funnel after the end of the casting, shell or funnel; cooling and crushing this slag; removing a base metal from the crushed slag; and crushing the slag to a size preferably less than 50 mm. These slags are placed in the feed hopper 8 above the oven and are quantitatively cut and added to the dephosphorization oven 1. However, among the recycled slag, the secondary refining slag contains a large amount of ALO3 which causes a slag foam. Therefore, when the suppression of the foam from the slag foam is preferably necessary, it is preferred that the decarburization slag is preferably used. In addition, in the modality, since the addition (quantity and timing) of the auxiliary materials is controlled depending on the species of the auxiliary materials, multiple feeder deposits can be used. In this case, the step of adding auxiliary material includes a process for adding recycled slag and, optionally, it can also include a process for adding a solid oxygen source or a process for adding a massive CaO source described below. In the modality, a converter is used as the dephosphor furnace 1.

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11/46 [0030] Next, a nitrogen gas supplied from a tank of nitrogen gas 5 is used as a nitrogen gas and is blown out of the base through a base blowing blow 3 supplied in the base of the dephosphor furnace 1 for blowing fine limestone powder into a base 6 blowing tank (a fine powder base blowing tank) (stirring process).

[0031] In order to ensure a necessary stirring force for the dephosphoration reaction, a flow rate of nitrogen gas and fine limestone powder can be appropriately established. In particular, in the modality, when a stirring force applied to the pig iron P is controlled to be within a range between 1.2 kW / t and 10 kW / t, both desiliconization and dephosphorization can be more effectively performed even with a cast pig iron having a relatively high concentration of silicon. When the stirring force is less than 1.2 kW / t, the oxidation of silicon in the pig iron advances faster than the oxidation of phosphorus and, therefore, the dephosphoration reaction is not likely to occur. On the other hand, when the stirring force is greater than or equal to 1.2 kW / t, the oxygen activity of a slag S at an interface between the slag S and the pig iron P approaches an activity of oxygen determined according to the amount of FeO in the slag. Therefore, even when the silicon concentration in the pig iron P is high, the dephosphorization reaction is easy to occur.

[0032] The agitation force ε is defined by the following (Formula 1). [Expression 2]

0.0062x ^, x7 ^E *

In 1 + [0033] follows.

(Formula 1)

Here in this (Formula 1), the respective variables are like ε: a base blowing agitation force (W / t) applied

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12/46 to cast iron P

Qg: an amount of a base blowing gas (NL / min; including a cracked gas from a solid material (for example, a fine limestone powder))

T: a temperature of molten pig iron (K) at the time of departure from a base sopo

Tg: a temperature (K) of the base blowing gas before blowing

H0: a depth of sofro (distance from a liquid surface of the molten pig iron to a tip end of a base blowing mesquite; (m))

Wm: a weight of the pig iron P (including a charge fragment; (t)) [0034] Then an oxygen gas (a high pressure oxygen) supplied from an oxygen gas tank 4 is blown into a surface of the pig iron P through a top blow lance 2 inserted in the dephosphorization oven 1; and dephosphorization begins (a process of blowing oxygen gas). In addition, depending on the state of the overflow, the blowing of oxygen gas from the top blowing boom 2 is used as a carrier gas to blow the fine powder of quicklime (for example, as illustrated in FIG. 6, a quicklime classified in a size of 2 mm to 200 mm) in a top blowing tank 7 (a fine lime powder top blowing tank) to the surface of the pig iron P (a process of adding fine powder of quicklime).

[0035] That is, high pressure oxygen is supplied from the oxygen gas tank 4 to the top blowing boom 2 via a tube, but the top blowing tank 7 is disposed between the gas tank 4 oxygen and the top blow boom 2. Therefore, the fine powder of quicklime can be blown onto the surface of the cast iron junPetition 870180045283, of 28/05/2018, pg. 17/60

13/46 with oxygen gas. As illustrated in a Gantt chart in the top section of FIG. 3 as an example, plural processes of the auxiliary material addition process (for example, the recycled slag addition process), the stirring process, the oxygen gas blowing process, and the fine powder addition process of quicklime are carried out in an overlapping time zone.

[0036] In the modality, in this way, a source of fine powder of quicklime is supplied from the top blowing lance to an ignition point formed on the cast iron surface. As a result, a molten calcium ferrite (CaO-FeO) is carried out at the ignition point; the formed calcium ferrite quickly reacts with SiO2 in the slag to form fine dicalcium silicate (2CaO-SiO2); and 2CaO-SiO2 having a high melting point is developed at the same time as dissolving phosphoric acid and is macroscopically and uniformly dispersed in the slag. Therefore, since 2CaO-SiO2 increases a practical solid phase rate of the slag and suppresses frothing due to the bridging effect, an overflow suppression effect that causes a production impediment is exhibited.

[0037] Overflow suppression using this method is particularly effective in a case where the dephosphorization of an elevated Si molten pig iron is carried out within a short period of time, a case where the secondary refining slag containing Al2O3 which promotes slag foam is recycled, or a case where a large amount of converter slag (the decarburization slag) is recycled.

[0038] Recently, recycling of construction waste has progressed and most construction waste had a tendency to be used as a construction material. Therefore, a demand to reduce the amount of discharge outside the system of a slag, which is used as the construction material, was increased 870180045283, of 05/28/2018, p. 18/60

14/46. In order to reduce the amount of discharge outside the slag system, it is more effective to recycle CaO in the slag, that is, to recycle the slag produced in post-processing subsequent to the dephosphorization process. However, due to the reason described below, it is not so easy to reuse the slags, produced in the post-processing, in the process of dephosphorization of molten pig iron. [0039] This is generally in the melting pig iron dephosphoration reaction, since the phosphorus in the pig iron is oxidized and removed to a slag, it is necessary that a source of oxygen and oxygen ions be applied to the phosphorus in the iron molten pig iron; and phosphate ions are stably produced in the slag (in this case, the oxygen ions are supplied to an interface between the molten pig iron and the slag by a basic oxide such as CaO that forms the molten slag). As the oxygen source, a solid oxide source such as an iron oxide and an oxygen gas can be used. In (Formula 2) to (Formula 4), the underlined chemical components (P, C, Si) represent chemical components in the pig iron (in the metal); and the chemical components in parentheses ((O ^2- ), (PO4 ^3- ), (SiO2)) represent chemical components in the slag.

2P + 5O + 3 (O ^2- ) = 2 (PO4 ^3- )

C + O = CO

Si + 2O = (SiO2) (Formula 2) (Formula 3) (Formula 4) [0040] An initial phosphorus concentration in molten pig iron is approximately 0.1%, but an initial carbon concentration in molten pig iron is greater than or equal to 4% (40 times the initial phosphorus concentration). Therefore, the decarburization reaction represented in (Formula 3) inevitably occurs, thereby generating CO gas. Due to this CO gas, the slag foam occurs. When this defoaming becomes severe, the so-called overflow phenomenon in which the slag overflows from the oven is

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15/46 caused to occur. When overflow occurs, there are problems with the fact that the rate of oxygen supply is reduced; an oxygen supply is interrupted and processing is inevitably interrupted; processing time is extended; and productivity deteriorates.

[0041] However, when slags produced in post-processing such as decarburization slag and secondary refining slag are recycled as a source of CaO in the dephosphorization process, these slags contain high concentrations of SiO2 and ALO3 other than CaO that are effective for dephosphorization, thereby increasing the amount of slag. Therefore, the overflow problem described above becomes significant. In addition, for example, as described in Non-Patent Document 1, Al2O3 significantly promotes slag foam. In particular, when it is necessary for the operation to be completed within a short period of time, it is difficult to reuse cast pig iron with a high silicon concentration in the dephosphorization process. The reason is that, when the silicon concentration in the pig iron is high, the amount of SiO2 produced in the desiliconization reaction is large and, thus, the total amount of slag produced is increased.

[0042] To address this, the present inventors have carefully investigated and solved the problems described above by supplying the fine powder of quicklime to an ignition point, formed in the molten pig iron, together with the top blowing oxygen in a while appropriate. At the high temperature flash point, first, the CaO-FeO fusion is formed; the fusion of CaO-FeO, formed at the ignition point, reacts with SiO2 in the slag to quickly form particles of 2CaO-SiO2; and these 2CaO-SiO2 particles are developed and are suspended in the slag. The present inventors clarified that

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16/46 the suspended 2CaO-SiO2 particles have a high effect of suppressing the slag foam described above. As a result, it was clarified that, even when pig iron with a high silicon content is dephosphorylated, recycled slag such as decarburization slag and secondary refining slag can be used.

[0043] One factor that has the greatest effect on the amount of slag generated in the dephosphorization process is the concentration of silicon in the pig iron. In the dephosphorization process, since the desiliconization reaction represented in (Formula 4) occurs, the degree of the amount of CaO to the amount of SiO2 produced in the desiliconization reaction, that is, the basicity is reduced. In order to maintain the slag's dephosphorization capacity, it is necessary that the basicity of the slag is maintained at approximately 2. When the concentration of silicon in the molten pig iron is high, the amount of CaO added to the slag is increased in proportion to the concentration of silicon in cast iron. In addition, when the slag produced for post-processing subsequent to the dephosphorization process is used as a source of CaO, the slag contains chemical components other than CaO such as SiO2, AbO3, MnO, and FeO. Therefore, the chemical components other than CaO are increased in the dephosphor furnace, the amount of slag production is greater than that of a case using a primary CaO source such as quicklime. As a reference, the amount of slag Ws (t) generated in the dephosphorization process is substantially represented in the following (Formula 5) when only quicklime is used as a source of CaO.

Ws = [% Si] x60x1000 / 28 / 100x [1+ (C / S)] xWm '(Formula 5) [0044] In the formula, [% Si] represents the silicon concentration (% by mass) of pig iron molten; (C / S) represents the target basicity of the slag after the dephosphorization process (= (% CaO) / (% SiO2);

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17/46 (-)); (% CaO) represents the CaO concentration (mass%) of the slag after the dephosphorization process; (% SiO2) represents the concentration of SiO2 (% by mass) of the slag after the dephosphorization process; and Wm 'represents the amount of molten pig iron (other than a charge fragment; (t))).

[0045] On the other hand, when decarburization slag, secondary refining slag, and the like are used as recycled slag, the amount of slag Ws (t) generated in the dephosphorization process is represented in the following (Formula 6).

Ws = [% Si] x60x1000 / 28 / 100x [1 +100 (C / S) x (Xi / 100 + X2 / (% CaO) LD + X3 / (% C aO) sR)] ^x Wm '(Formula 6 ) [0046] In the formula, ξ1 represents the (-) ratios of fine quicklime powder in the total CaO amounts, ξ2 represents the (-) decarburization slag ratios in the total CaO amounts, and ξ3 represents the ratios (- ) the amount of CaO in the secondary refining slag, respectively; (% CaO) LD represents the CaO concentration (mass%) in the decarburization slag; and (% CaO) sR represents the concentration of CaO (% by mass) in the secondary refining slag.

[0047] In addition, generally, [% X] represents the percentage of mass of chemical component X in metal (in this case, molten pig iron); and (% X) represents the percentage of mass of chemical component X in the slag.

[0048] In this case, the chemical compositions of the decarburization slag and the secondary refining slag are, for example, as shown in Table 1. In the secondary refining slag, the chemical composition (the quantities of chemical components such as CaO and Al2O3 ) varies a lot. In addition, since Al deoxidation is carried out on molten steel during secondary refining, the Al2O3 concentration is high and the CaO concentration is relatively low.

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18/46 low in secondary refining slag. Therefore, when only secondary refining slag is reused as a source of CaO for dephosphorization, the amount of slag is 2 to 3 times that of the case of using only fine lime powder as a source of CaO; the overflow described above becomes severe; and the real operation is difficult to perform.

[0049] On the other hand, when fine quicklime powder is used as a part (preferably within a range between 25% and 90% and more preferably within a range between 25% and 80% (for example, approximately 30 %)) of a CaO source needed to control the slag basicity; this fine powder of quicklime is blown to the ignition point at a high temperature of approximately 2000 ° C together with a top blowing oxygen gas. As a result, the liquid phase rate of the slag is reduced and, thus, the slag foam can be effectively suppressed. [0050] In this case, first, the calcium ferrite is produced from the fine powder of quicklime at the ignition point; and this calcium ferrite is transferred into the slag and is changed into solid dicalcium silicate particles while rapidly dissolving SiO2 and phosphoric acid in the slag. In addition, dicalcium silicate particles are developed at the same time as fixing a liquid slag between the dicalcium silicate particles, thereby forming a granular slag. As a result, the effect of substantially reducing the liquid phase rate of the slag can be obtained.

Table 1 (mass%)

Dog SiO2 MnO MgO P2O5 Al2O3 T-Fe Slag of carboni- zation 49.1 11.6 5.5 5.6 2.1 3.1 17.8

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19/46 (mass%)

Dog SiO2 MnO MgO P2O5 Al2O3 T-Fe Slag secondary refining 31.2 11.2 8.7 7.9 0.8 18.0 14.2

[0051] By the way, in Patent Document 2, the present inventors describe a method of suppressing defoaming by reducing the liquid phase rate of a slag in which the basicity of the slag is controlled to 1.2 or more and less than 2 , 5 using a CaO source having a particle size less than 5 mm. However, in this method, since quicklime, from which basic slag can be easily controlled, is used in an amount of 15.5 kg per 1 ton of cast iron, there is a problem with the fact that the cost is much bigger. In particular, in order to crush the quicklime, a large amount of energy is required. When the total amount of 15.5 kg / t of quicklime has an average particle size of less than 5 mm (in particular, fine quicklime powder), the cost is significantly higher. Conversely, when a massive quicklime having an average particle size of 5 mm or larger is used in the dephosphorization process, there is a case where the melting rate of the massive quicklime in the slag may deteriorate; and the effectiveness of dephosphorization can deteriorate.

[0052] When the slags produced in the post-processing are used in the dephosphorization process, the slag volume is significantly increased; and the ALO3 contained in the recycled slag promotes foaming. Therefore, when recycled slag is used in the method described in Patent Document 2, the cost is significantly higher due to an increase in the amount of fine lime powder used; and a considerable amount of liquid phase remains in the slag, which promotes foaming. When recycled slag is used, in order to increase the rate of dephosphorization,

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20/46 generally, a large amount of solid quicklime is added simultaneously to increase basicity.

[0053] On the other hand, in the modality, the fine powder of quicklime is supplied to the high temperature flash point in an appropriate time. As a result, while suppressing the amount of fine quicklime powder used to an appropriate amount, the dephosphorizing effect and defoaming suppression caused by the fine quicklime powder can be sufficiently ensured. That is, as described above, a liquid phase of calcium ferrite is instantly formed, and then 2CaO-SiO2 is formed. Whereas 2CaO-SiO2 is included in a liquid slag phase between them while dissolving the phosphoric acid; and are developed into the fine fine powder having a particle size of a maximum of 10 mm and several tens of mm as a whole, defoaming is suppressed, that is, the desorbing property of air bubbles in the slag is significantly improved.

[0054] In addition, recycled slags having a low melting point are supplied to the surface of the pig iron (optionally, pig iron containing a fragment) in the initial (beginning) stage of the dephosphorization process. Therefore, when comparing a case where only massive quicklime is supplied, an early stage fusion, which is effective to simultaneously perform desiliconization and dephosphorization, can be quickly formed. In addition, since recycled slag can quickly supply CaO in the slag in cast pig iron, the cost can be reduced without compromising the effectiveness of the simultaneous dephosphorization and desiliconisation process. In addition, due to the supply of recycled slag and the supply of fine quicklime powder at an appropriate time, CaO can be efficiently used for dephosphorization. Therefore, the amount of slag discharge in the total steelmaking processes can be reduced 870180045283, dated 05/28/2018, p. 25/60

21/46 zida; and a dephosphorating slag having almost no free lime, which can be directly used as a building material can be obtained.

[0055] The present inventors determined that, if the desiliconization and dephosphorization were simultaneously carried out as in the case of the modality, the concentration of silicon in the molten pig iron would be reduced to almost zero; gradually, the decarburization reaction would preferably be carried out; and the rate of generation of CO gas, generated in the reaction of (Formula 3) would be increased, which would cause a problem of defoaming of the slag. Therefore, the present inventors have found that the time in which the fine powder of quicklime is added after the silicon concentration is sufficiently reduced is more preferable. Specifically, as illustrated in FIG. 3, the process of supplying the fine powder of quicklime as a source of CaO together with the oxygen gas that blows to the surface of the pig iron begins after the time (start time) when the concentration of silicon in the pig iron melt is reduced to 0% by mass or more and to 0.15% by mass or less. In order to suppress the amount of fine lime powder used to a minimum, it is preferred that this start time is the same in which the concentration of silicon in the pig iron is reduced to 0% by weight or more and 0.08 Bulk% or less. It is preferred that the concentration of silicon in the pig iron at that start time is greater than or equal to 0% by mass. However, when considering the rate of CO gas generation by decarburization reaction, the concentration of silicon in the pig iron at that start time may be greater than or equal to 0.001% by mass or greater than or equal to 0, 01% by mass. In this way, the rate of desiliconization reaction is reduced according to (Formula 4); and the rate of dephosphorization is improved according to (Formula 2) in a timing in which the rate of dismissal reaction 870180045283, of 05/28/2018, p. 26/60

22/46 carburization is increased according to (Formula 3). As a result, a time zone in which defoaming causes a problem is significantly reduced; and desiliconisation and dephosphorization can be carried out effectively while suppressing defoaming.

[0056] As described above, by controlling the timing in which the fine powder of quicklime is supplied, the amount of a fine powder of expensive quicklime used can be reduced and the large amounts of decarburization slag and refining slag secondary can be used.

[0057] The silicon concentration in the pig iron described here can be obtained from a real operating data set or a simulation under various operating conditions such as the silicon concentration in the early stage pig iron.

[0058] In the modality, as a source of CaO, primary sources of CaO such as quicklime (including CaO as a major component), an extinct lime (including Ca (OH) 2 as a major component), and limestone ( including CaCO3 as a major component); and recycled slag such as decarburization slag and secondary refining slag are used. In addition, the fine powder of quicklime that is supplied together with the oxygen gas is fine powder having a maximum particle size of 500 mm or less and a raw material derived from an ore (ie, a raw material that is obtained after thermal decomposition and has a chemical composition composed of impurities such as CaO and a gangue). The examples of the measurement results of the particle size distribution of fine quicklime powders used in the examples and comparative examples described below (a volume frequency distribution and a cumulative distribution of the same measured by a particle size distribution analyzer of laser diffraction) are illustrated

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23/46 in FIG. 6. In this example, the particle size is in a range of 2 mm to 200 mm. As the particle size becomes larger, the effectiveness of contact between chemical components related to dephosphorization deteriorates. Therefore, it is necessary that the maximum particle size of fine quicklime powder is less than or equal to 500 mm. In addition, when the maximum particle size of fine lime powder is excessively large (for example, greater than 500 mm), a portion of the tube is extremely used, which is not preferable. On the other hand, the lower limit of the maximum particle size of fine quicklime powder is not particularly limited. By setting the lower limit so that it is not excessively low, the crushing cost and loss of dispersion, which can be caused by the absorption of fine lime powder from the blowing gas, can be reduced. Therefore, the maximum particle size of fine lime powder can be greater than or equal to 1 mm. In order to prevent the generation of unnecessary gases and energy loss in the slag, fine powder of quicklime is used (including CaO as a main component (eg 90% by mass or greater)) as a source of CaO that is supplied together with oxygen gas.

[0059] In addition, the average particle size of the fine limestone powder used for the base blow is preferably 32 mm to 75 mm. This fine limestone powder is used primarily for stirring, although it also functions as a source of CaO.

[0060] In addition, in order to finely adjust the basicity, a source of massive CaO (for example, primary CaO sources) derived from an ore can be supplied from feeder 8. However, unless the fine adjustment of the basicity is necessary, it is preferred that the massive CaO source is not used as much as possible to increase the recycling rate of recycled slag and increase the efficiency of use of the CaO sources. Specifically, the

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24/46 amount of the massive CaO source having an average particle size of 5 mm or greater per 1 ton of cast iron is preferably limited to less than or equal to 7.5 kg, more preferably limited to less than which is equal to 7.0 kg or less than or equal to 5.0 kg, even more preferably limited to less than or equal to 1 kg, and more preferably limited to 0 kg. In addition, when the source of massive CaO is supplied in the dephosphor furnace, the process of adding a massive CaO source can begin at the same time as the process of adding recycled slag.

[0061] In addition, taking into account the control of the basicity of the slag and suppression of the defoaming, it is preferred that the amount of fine quicklime powder (in case of not adding massive quicklime) or the total amount of fine powder of quicklime and the source of massive CaO are limited to less than or equal to 3.2 kg per 1 kg of Si in the pig iron.

[0062] Furthermore, when the silicon concentration in the pig iron at the time of the start of the recycled slag addition process is less than 0.6% by mass, it is preferred that only the secondary refining slag or both the decarburization slag as well as secondary refining slag are used; and it is more preferable that both decarburization slag and secondary refining slag are supplied to the pig iron.

[0063] On the other hand, when the silicon concentration in the pig iron at the time of starting the process of adding recycled slag is greater than or equal to 0.6% by mass, it is preferred that only the decarburization slag be supplied to the pig iron.

[0064] Using recycled slag as described above, recycled slag can be used with a high efficiency and balance while suppressing the slag foam

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25/46 to the minimum.

[0065] The concentration of the beginning of the initial stage (before blowing the oxygen gas) in the molten pig iron of the dephosphorization oven that is applied to the modality, is not particularly limited. For example, the onset of early-stage concentration may be greater than or equal to 0.3% by mass, greater than or equal to 0.4% by mass, or greater than or equal to 0.5% in pasta.

[0066] In the modality, as described above, recycled slag is reused.

[0067] As a result, the amount of slag discharge in integral steelmaking processes can be reduced; and desiliconization and dephosphorization can be carried out simultaneously while suppressing the slag foam. In addition, in the modality, as an example of modification, when a steel product containing Mn is produced as described below, the cost required to control the amount of Mn can be suppressed using a slag containing MnO as a recycled slag. In the modification examples described below (a first modification example and a second modification example), since a partial configuration is the same as that of the modality, the description of such a configuration will not be repeated.

[0068] As a steel product containing Mn, demand for a steel product such as a high tensile strength steel plate has increased. In such a steel product, the amount of Mn contained in the steel product is regulated according to the product specification. When adjusting the Mn content in steel, only the Mn contained in the pig iron as a main component is used, and the amount of Mn is insufficient. Therefore, a final adjustment for the addition of the Mn alloy is carried out during the period of a primary adjustment for the addition of an Mn ore to the steel during the decarburization blow (the

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26/46 decarburization furnace) or the decarburization blow finish (when the molten pig iron is extracted from the decarburization furnace to a steel shell) for the finishing of the secondary refining.

[0069] In addition, as described in Patent Document 3, an Mn ore is also added to the pig iron in the pig iron pretreatment. In this case, when steel products containing Mn according to the production specification are produced, a large amount of an Mn ore or Mn alloy is required and the cost is increased. On the other hand, in the process of desiliconization and dephosphorization, when a slag containing MnO is used instead of an Mn ore, the cost is effectively reduced. [0070] FIG. 2 is a diagram illustrating an example of a basic process when the molten pig iron desiliconisation and dephosphorization method is applied to the steel industry. As illustrated in FIG. 2, the process of desiliconization and dephosphorization of the pig iron (corresponding to the modality) is carried out in the dephosphorization furnace; the decarburization blow is carried out in the decarburization furnace; secondary refining is carried out; molten steel is prepared from molten pig iron; and molten steel is continuously melted to produce steel. When steel products containing Mn are produced, the amount of MnO is likely to be greater in a slag (ie, secondary refining slag) discharged in secondary refining or in continuous casting between the slag discharged in the processes described above. Therefore, in the process of desiliconisation and dephosphorization of molten pig iron, it is preferred that the secondary refining slag containing Mn is returned and added to the molten pig iron of the dephosphorization furnace (the first example of modification). In addition, particularly when an Mn ore is added to the decarburization furnace, it is preferred that

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27/46 the decarburization slag containing Mn as well as the secondary refining slag is returned and added to the molten pig iron of the dephosphorization furnace (the second modification example). [0071] Thus, in the first example of modification of the modality, the secondary refining slag (at least one of a cup slag and a funnel slag) is returned and placed in the dephosphorizing furnace 1. When the steel products containing Mn are produced, the secondary refining slag contains Mn. However, as described above, the secondary refining slag contains a large amount of AHO3. Therefore, when the secondary refining slag is placed in the dephosphorization furnace, the slag foam is significantly promoted and in this way the overflow phenomenon in which the slag and pig iron overflow from the furnace is caused to occur. Thus, due to operational problems, the technique of placing the secondary refining slag in the dephosphorating slag has not yet been put into practice.

[0072] As described above, in the first example of modification of the modality, the secondary refining slag is added to the molten pig iron; and the fine powder of quicklime is blown onto the surface of the pig iron together with the top blowing oxygen gas. As a result, 2CaO-SiO2 is rapidly formed at the hot spot (an ignition point) on the surface of the pig iron; and the liquid phase rate of the slag is reduced. Therefore, since the slag fluidity deteriorates and the overflow phenomenon is difficult to occur, secondary refining slag can be added in the process of desiliconization and dephosphorization. Meanwhile, the concentration of MnO in the slag liquid phase is increased due to a reduction in the slag liquid phase rate. Consequently, while reducing a rate of distribution (that is, (% of MnO) / [% of Mn]) from MnO in the slag to Mn in the cast iron pig iron 870180045283, of 28/05/2018, p. 32/60

28/46 do, the Mn concentration in the pig iron can be improved by transferring the Mn in the secondary refining slag to the pig iron; or the transfer of Mn in the pig iron to the secondary refining slag by oxidation can be suppressed. Since the amount of CaO in the secondary refining slag varies widely, there is an amount where the effect as a substitute for a dephosphorating agent may be less than that of quicklime.

[0073] The amount of secondary refining slag added to the pig iron is preferably within the range of 0.1 kg / t to 16 kg / t. When the amount of secondary refining slag added is excessively small, the effect of improving the Mn concentration in the pig iron cannot be sufficiently achieved when compared to the related technique. Conversely, when the amount of secondary refining slag added is excessive, the amount of slag in the process of desiliconisation and dephosphorization is increased and thus the overflow phenomenon is likely to occur. In this case, in order to suppress the overflow phenomenon, a large amount of fine powder of quicklime is required.

[0074] In the first modification example described above, only the secondary refining slag is added to the dephosphorization furnace. However, in the example of secondary modification, in addition to the secondary refining slag, the decarburization slag, produced in the molten pig iron decarburization blow process after the desiliconization and dephosphorization process described below and illustrated in FIG. 4, is also added to the dephosphorization furnace. Since this decarburization slag also contains MnO, similar to the first modification example, the concentration of Mn in the pig iron can be improved by transferring Mn in the

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29/46 slag for cast pig iron; or the transfer of Mn in the pig iron to the secondary refining slag by oxidation can be suppressed. Since other configurations in the second modification example are the same as those in the first modification example, except that the decarburization slag is used as a recycled slag, the description will therefore not be repeated.

[0075] In the following, the reason why the placement of the secondary refining slag in the dephosphorization furnace is effective in the modification examples described above (the first modification example and the second modification example) will be described based on the flow chart illustrated in FIG. 2. FIG. 1 is a diagram illustrating the process of desiliconization and dephosphorization in the dephosphorization furnace, and FIG. 4 is a diagram illustrating the decarburization blow in the decarburization furnace.

[0076] A solid auxiliary material containing at least the secondary refining slag is added from the feed hopper 8, which is supplied above the dephosphorizing oven 1, to the cast pig iron P. In addition, optionally, a blowing stream of base (for example, the fine limestone powder described above) is blown out of the base blowing pebble 3, which is supplied at the base of the dephosphor furnace 1, for the pig iron P together with the gases such as a combustible gas, an oxygen gas, and an inert gas; and the pig iron P is stirred. Then, the oxygen gas is blown from the top blow lance 2 to the surface of the pig iron P; and a source of CaO acts as the desiliconization and dephosphorizing agent. As a result, desiliconization and dephosphorization are carried out simultaneously. In the dephosphorization furnace 1, Si and P in the molten pig iron are transferred to the slag and, thus, the concentration of Si and the concentration of P in the molten pig iron are reduced.

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In addition, the molten pig iron in which the Mn concentration is improved when compared to the related technique is transported to a decarburization furnace 10 illustrated in FIG. 4, followed by the decarburization blow. A feed hopper 15 is provided above the decarburization furnace 10. A solid auxiliary material (eg, quicklime or ore) is added from feed hopper 15 to a PLD cast iron. In the modification examples described above, like this auxiliary material, a necessary amount of Mn ore is used in order to increase the concentration of Mn in the cast iron Pld to be in the production specification range. However, since the concentration of Mn in the Pld pig iron of the initial stage of the decarburization furnace 10 is increased when compared to the related technique, the required amount of Mn ore is significantly reduced when compared to the related technique. Consequently, the amount of an expensive Mn ore or Mn alloy, which is used during decarburization blowing or secondary refining, is reduced when compared to the related technique, and thus the cost can be reduced. After the auxiliary material is added to the cast pig iron PLD, in the decarburizing furnace 10, a gas in a base blowing gas tank 13 is blown from a base blowing blast 14, which is supplied in the decarburizing furnace base. 10, for cast pig iron PLD. Then, an oxygen gas in an oxygen gas tank 12 is blown from a top blowing boom 11 into the PLD cast pig iron, thereby performing the decarburization blow. [0078] The molten steel produced by the decarburization blow is transferred to the secondary refining process to adjust chemical components in the molten steel during secondary refining. The molten steel after secondary refining is transported to a continuous casting machine, and steel such as a slab is produced at

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31/46 from cast steel. In FIG. 2, the recycled slag is added to the dephosphorization furnace of the same strain. However, recycled slag can also be added to the dephosphorization furnace from a different line from the dephosphorization furnace that is applied to the modality described above and the examples of modification thereof.

[0079] Unlike the modality, it can also be considered that the secondary refining slag is added to the decarburization furnace 10 instead of the dephosphorization furnace 1. However, in the decarburization furnace, the concentration of C in the pig iron is lower than that of the dephosphorization oven; and the concentration of an oxidation atmosphere is high. Therefore, the MnO to Mn reduction reaction is not likely to occur and an Mn production is low. In addition, in order to recycle Mn in recycled slag, it is necessary that recycled slags contain Mn (ie MnO). That is, during Mn recycling, the concentration of MnO in the recycled slag is necessarily greater than 0%, preferably greater than or equal to 6.0%, and more preferably greater than or equal to 10%. The upper limit of the concentration of MnO in recycled slag is not particularly limited, however, for example, it can be 25% when considering the amount of CaO in the slag.

[0080] The modality described above and the examples of modification thereof include the process of blowing oxygen gas blowing oxygen gas from a furnace top towards a cast iron surface; the process of adding recycled slag to supply at least one of a decarburization slag and a secondary refining slag to the cast iron surface as a recycled slag; and the process of adding fine quicklime powder supplying the fine quicklime powder having a maximum particle size of 500 mm or less together with the flue gas.

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32/46 oxygen that blows to the surface of the pig iron. Among these processes, the process of adding fine powder of quicklime starts at a starting time in which a concentration of silicon in the pig iron is reduced to 0% by weight or more and 0.15% by weight or less. Therefore, in the modality described above and in the examples of modification thereof, desiliconization and dephosphorization can be performed simultaneously with high efficiency while reducing the amount of total slag discharge in the integral steel processes.

[0081] In addition, in the modification examples described above, recycled slags containing Mn are used. Therefore, even when steel products containing Mn according to the production specification are produced, the amount of an Mn ore or Mn alloy used can be reduced when compared to the related technique and thus an increase in cost can be suppressed. [0082] In the related technique, when the silicon concentration in the pig iron is greater than 0.3%, the total amount of slag, generated during the dephosphorization and desiliconization process, the decarburization blowing process, and the process secondary refining process as illustrated in FIG. 5, is approximately greater than 100 kg / t per 1 ton of processed pig iron. However, by adopting the modality and the modification examples, even when the silicon concentration in the pig iron is 0.5%, the total amount of slag can be suppressed to be less than 100 kg / t. The amount of slag discharge shown in FIG. 5 is the total amount of slag, which is not recycled in the desiliconization and dephosphorization process, between a slag (a dephosphorization slag) generated in the desiliconization and dephosphorization process, the decarburization slag, and the secondary refining slag. In addition, each of the numerical values of the captions in FIG.

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33/46 represents ξ1, ξ2, and ξ3 (Formula 6) in order from left to right, respectively.

[0083] In addition, the slag from dephosphorization generated in the modality and in the examples of modification thereof has almost no free lime. Therefore, even when a steam aging process or an air aging process over a long period of several months is not performed as in the related technique, the water immersion expansion rate, which is measured with a defined measurement method on JIS A5015, it is extremely low at 0.5% or less. In addition, in a case where a dephosphorating slag is finally crushed and immersed in pure water when the water to slag ratio 5: 1, in the dephosphorating slag of the related technique having a high free lime concentration, the pH is approximately 12.5; however, in the dephosphoration slag generated in the modality and in the examples of modification thereof, the pH is reduced to approximately 11. Consequently, the dephosphoration slag generated in the modality and in the examples of modification thereof can safely be used as a building material. .

Examples [0084] In all examples 1 to 14 and comparative examples 1 to 3 described below, the following processes were performed. A converter-type furnace was loaded with the predetermined amounts of pig iron and scrap. Then, a nitrogen gas and the fine powder of calcium carbonate (the fine powder of limestone) were blown from the base of the oven; and the oxygen gas was blown from a main lance while adding an auxiliary material (Initial Stage Top Addition Flow in table 3) from a feeder tank provided above to the furnace, thereby performing a dephosphorization process. The deterioration in the basicity of scoria,

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34/46 caused by desiliconization, is canceled with the addition of a CaO source to adjust the slag basicity in the dephosphorization process. Decarburization slag and secondary refining slag having the chemical compositions (slag compositions) shown in table 1 were used.

[0085] In examples 1 to 14, as the CaO sources to be added from above, recycled slag such as secondary refining slag and decarburization slag were supplied in the oven; and fine quicklime powder was supplied to an ignition point along with the top blowing oxygen gas.

[0086] Calcium carbonate, which was blown from the base of the furnace into the pig iron, generated CO gas with the reaction according to (Formula 7) and contributed to the stirring (C represents C in the pig iron).

CaCO3 + C = CaO + 2CO (Formula 7) [0087] In examples 1 to 9 shown in tables 2 to 4, at least one of the secondary refining slag and the decarburization slag was used as the recycled slag; and an amount of C [% of C], an amount of Si [% of Si], and an amount of P [% of P] in the pig iron before and after the dephosphorization process were measured. In these examples, the concentration of silicon can be reduced substantially to 0% and the concentration of phosphorus can be sufficiently reduced to approximately 0.1% to 0.035%.

[0088] In example 4 (the concentration of Si in the pig iron was approximately 0.15%), by properly controlling the start time of supply of fine quicklime powder, a large amount of phosphorus can be removed from the iron molten pig iron for slag compared to comparative example 2 where the quantities of recycled slag and fine lime powder used were in the

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35/46 same level. Likewise, in examples 1 to 3 (the Si concentration in the molten pig iron was approximately 0.08%), by controlling the start time of supplying fine lime powder more appropriately, a large amount of phosphorus can be removed from cast pig to slag compared to examples 4 to 6 where the quantities of recycled slag and fine lime powder used were at the same level.

[0089] In addition, when the concentration of silicon in the pig iron (an early-stage pig iron) at the time of the addition of the recycled slag was greater than or equal to 0.6%, in example 3, only decarburization slag was used; and in this way, a large amount of phosphorus can be removed from the pig iron cast to the slag compared to example 7 in which both the secondary refining slag and the decarburization slag were used.

[0090] In addition, in examples 1 to 3, by reducing the amount of solid quicklime, a large amount of recycled slag can be efficiently used at the same level as the target basicity compared to example 8.

[0091] In addition, in examples 1 to 3, since a more sufficient stirring force was applied to the pig iron, examples 1 to 3 can be desirably applied to the pig iron containing a large amount Si. In addition, a a large amount of phosphorus can also be removed from pig iron for slag compared to example 9.

[0092] On the other hand, in comparative example 1, as in the case of the related technique, solid quicklime having an average particle size of approximately 20 mm was used in combination with decarburization slag and secondary refining slag without using the fine powder of quicklime, but the overflow was severe. PortanPetição 870180045283, of 05/28/2018, p. 40/60

36/46 to, in order to promote the sedimentation of the slag, it was necessary that the dephosphorization process was interrupted for 5 minutes and in this way, the productivity significantly deteriorated. In addition, the slag overflowed from the oven and an iron loss was increased. In addition, when the dephosphorization process was interrupted, that is, when the supply of oxygen gas was interrupted, the FeO in the slag was reduced by the carbon in the molten pig iron. Therefore, the oxidizing force in the kiln has deteriorated and the capacity for dephorylation (the amount of dephosphorization) has deteriorated. When the amount of oxygen is increased in order to compensate for the deterioration in the dephosphorization capacity, the decarburization reaction advances more than necessary and, thus, the melting point of the pig iron is increased. As a result, the amount of a base metal connected to the oven can be increased; or a base metal can be attached to the shell after being extracted from the oven into the shell.

[0093] Furthermore, in comparative example 2, since the supply of a relatively expensive fine quicklime powder started at the time when dephosphorization and desiliconization competed against each other, the fine quicklime powder could not be sufficiently used during high efficiency dephosphorization.

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Table 2

Iron pig molten Wm ' Suca- OK Total amount of materials raw Oven internal diameter Ho Oven capacity V V / Vm ' Nitrogen gas CaCÜ3 and Top blowing oxygen unity t t t m m m ³ m ³ / t Nm ³ / h Kg / min kW / t Nm ³ / h Example 1 263 31 294 4.9 2.23 180 0.68 400 100 3,310 14000 Example 2 263.7 20 284 4.9 2.15 180 0.68 400 100 3,275 14000 Example 3 269 32 301 4.9 2.28 180 0.67 400 200 6,111 16000 Example 4 264 20 284 4.9 2.15 180 0.68 400 100 3,369 14000 Example 5 276 23 299 4.9 2.27 180 0.65 400 100 3,311 14000 Example 6 267 23 290 4.9 2.20 180 0.67 400 200 6.067 16000 Example 7 268 23 291 4.9 2.20 180 0.67 400 200 6,130 15000 Example 8 277 15 292 4.9 2.21 180 0.65 400 100 3,364 14000 Example 9 274 14 288 4.9 2.18 180 0.66 300 20 0.889 13000 Ex. Comp. 1 270 25 295 4.9 2.23 180 0.67 400 100 3,232 14500 Ex. Comp. 2 267 26 293 4.9 2.22 180 0.67 400 100 3,278 14000

9WZS

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Table 3

Quicklime powder f initial stage top addition flow Delivery fee delivery time quantity dade total start of supply [% Si] massive quicklime decarburization slag secondary refining slag iron ore basics- dade target *1 unity kg / min min kg / t kg / t kg / t kg / t kg / t Example 1 500 4.4-11.8 12.5 0.072 0.0 11.1 3.8 18.5 1.93 Example 2 500 4.0-12.2 14.5 0.079 0.0 0.0 16.0 17.0 1.96 Example 3 500 2.4-13.8 19.0 0.077 0.0 23.9 0.0 21.2 1.99 Example 4 500 2.4-8.6 11.0 0.145 0.0 10.0 6.8 24.0 1.98 Example 5 500 3.1-13.3 17.0 0.143 0.0 0.0 17.0 28.6 1.95 Example 6 500 2.1-12.0 17.0 0.148 0.0 23.4 0.0 19.5 1.93 Example 7 500 3.0-14.1 19.0 0.075 0.0 16.0 6.2 21.2 1.98 Example 8 550 4.5-12.7 15.5 0.077 4.0 0.0 2.0 26.6 1.98 Example 9 686 9.9-14.1 10.0 0.079 0.0 6.0 3.0 15.0 1.91 Ex. Comp. 1 - - - - 12.5 11.0 8.0 19.0 1.93 Ex. Comp. 2 550 2.2-10.4 14.0 0.210 0.0 9.0 4.0 17.0 1.96

*1. Target basicity = (amount of total CaO added) / (total amount of S1O2 added + amount of S1O2 generated by oxidation of Si in the pig iron).

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Petition 870180045283, of 05/28/2018, p. 43/60

Table 4

Processing time cast iron composition cast iron temperature Note [%Ç] [% Si] [%P] unity min % % % ° C Example 1 13.9 Before the process 4.81 0.5 0.109 1375 After the process 3.55 <0.01 0.010 1348 Example 2 13.8 Before the process 4.74 0.48 0.101 1326 After the process 3.5 <0.01 0.011 1345 Example 3 14.3 Before the process 4.79 0.8 0.097 1372 After the process 3.59 <0.01 0.012 1348 Example 4 11.6 Before the process 4.38 0.42 0.093 1369 After the process 3.6 <0.01 0.032 1313 Example 5 12.2 Before the process 5.02 0.54 0.092 1392 After the process 3.85 <0.01 0.029 1320 Example 6 13.9 Before the process 4.39 0.75 0.103 1325 After the process 3.79 <0.01 0.027 1364 Example 7 14.5 Before the process 4.55 0.75 0.091 1345 After the process 3.79 <0.01 0.027 1354 Example 8 12.7 Before the process 4.87 0.55 0.092 1394 After the process 3.75 <0.01 0.030 1328 Example 9 14.1 Before the process 4.69 0.32 0.101 1370 After the process 3.84 <0.01 0.032 1320 Ex. Comp. 1 12.5 Before the process 4.69 0.49 0.107 1345 large pouring process interrupted for 5 minutes After the process 3.48 <0.01 0.045 1338 Ex. Comp. 2 14.5 Before the process 4.76 0.51 0.097 1358 After the process 3.52 <0.01 0.036 1346

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Petition 870180045283, of 05/28/2018, p. 44/60

40/46 [0094] As shown in tables 5 to 7, in examples 10 to 14 and comparative example 3, in addition to the [% C], [% Si], and [% P] described above, the amount of Mn [% Mn] in the pig iron before and after the dephosphorization process was measured. From the amount of Mn [% of Mn] after the dephosphorization process, the required amount of an Mn ore placed in the decarburization furnace (in terms of Mn in the pig iron in the decarburization furnace, Mn ore in the decarburization furnace) decarburization in table 7) was calculated. Generally, the amount of an Mn ore placed in the decarburization furnace was determined from an empirical value of a reduction rate of an Mn ore (ie, an increasing amount of [% Mn] due to an Mn ore) , a [% of Mn], and [% of Mn] final target before the decarburization process (that is, after the dephosphorization process). In Examples 10 to 14 and Comparative Example 3, at least one of the secondary refining slag and the decarburization slag was used as the recycled slag.

[0095] In examples 10 to 14, the concentration of silicon can be reduced substantially to 0% and the concentration of phosphorus can be sufficiently reduced to approximately 0.1% to 0.015%. [0096] In examples 11 to 14 where the secondary refining slag (the shell slag) having a sufficiently high MnO concentration was added to the dephosphorization furnace, the Mn concentration after the dephosphorization process was higher and the amount required of an Mn ore placed in the decarburization furnace was reduced compared to example 10 where the secondary refining slag was not used. In example 13, in addition to the secondary refining slag, the decarburization slag was also placed there.

[0097] In comparative example 3, the secondary refining slag, Petition 870180045283, of 05/28/2018, p. 45/60

41/46 ria (the cupped slag) was placed in the dephosphorating slag, but the fine powder of quicklime was not supplied to it. Therefore, in comparative example 3, high efficiency dephosphorization cannot be used at the flash point; and the amount of P removed from the pig iron for the slag was reduced compared to examples 10 to 14. Furthermore, in this case, in order to prevent overflowing, it was necessary that the amount of the secondary refining slag be placed limited as an insignificant amount; and the efficiency of reusing Mn in the secondary refining slag cannot be sufficiently achieved.

[0098] The target basicity in tables 3 and 6 was calculated according to (CaO) / (SiO2) the amount of CaO and the amount of SiO2 in all auxiliary materials (for example, CaCO ₃ , the fine powder of quicklime , solid quicklime, decarburization slag, secondary slag, and iron ore) added to the dephosphor furnace, and the amount of Si in the pig iron. That is, the target basicity is the value obtained by dividing the amount of total CaO in auxiliary materials (ie, the amount in terms of CaO) by the sum (that is, the amount in terms of SiO2) of the total amount of SiO2 in the materials auxiliaries and the total amount of SiO2 generated by the oxidation of Si in the pig iron. In addition, the process time in Tables 4 and 7 represents the supply time for which the supply of the top blowing oxygen gas to the dephosphorization furnace was continued; and does not include downtime for which the supply of the top blowing oxygen gas has been interrupted.

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Table 5

Iron pig molten Wm ' Suca- OK Total amount of materials raw Oven internal diameter Ho Oven capacity V V / Vm ' Nitrogen gas CaCÜ3 and Top blowing oxygen unity t t t m m m ³ m ³ / t Nm ³ / h Kg / min kW / t Nm ³ / h Example 10 264 19 283 4.9 2.14 180 0.69 400 100 3,378 14000 Example 11 263 20 283 4.9 2.14 180 0.69 400 100 3,378 14000 Example 12 260 203 283 4.9 2.14 180 0.69 400 100 3,392 14000 Ex. Comp. 3 264 19 283 4.9 2.14 180 0.69 400 100 3,378 14000 Example 13 267 20 287 4.9 2.17 180 0.67 400 100 3,338 14000 Example 14 270 20 290 4.9 2.17 180 0.67 400 100 3,338 14000

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Petition 870180045283, of 05/28/2018, p. 47/60

Table 6

Quicklime powder f initial stage top addition flow Delivery fee delivery time quantity dade total start of supply [% Si] massive quicklime decarburization slag secondary refining slag iron ore basics- dade target *1 unity kg / min min kg / t kg / t kg / t kg / t kg / t Example 10 500 4.1-11.5 13.0 0.078 0.0 14.0 0.0 22.5 1.93 Example 11 500 4.2-13.3 16.0 0.078 0.0 0.0 3.4 17.4 1.85 Example 12 500 4.0-12.5 15.0 0.078 0.0 0.0 6.9 23.0 1.92 Ex. Comp. 3 - - 0.0 - 17.0 0.0 2.5 22.5 1.94 Example 13 500 4.4-12.1 13.5 0.077 0.0 15.0 16.0 23.0 1.94 Example 14 500 4.1-10.8 11.5 0.079 3.5 0.0 16.0 25.0 2.07

*1. Target basicity = (total amount of CaO added) / (amount of total S1O2 added + amount of S1O2 generated by oxidation of Si to molten pig iron).

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Petition 870180045283, of 05/28/2018, p. 48/60

Table 7

Processing time cast iron composition cast iron temperature Mn ore in the decarburization furnace observe vation [%Ç] [% Si] [% Mn] [%P] unity min % % % % ° C kg / t Example 10 12.7 Before the process 4.38 0.50 0.20 0.093 1369 5.1 After the process 3.60 <0.01 0.117 0.012 1345 Example 11 14.0 Before the process 4.38 0.52 0.20 0.093 1369 4.8 After the process 3.56 <0.01 0.130 0.015 1345 Example 12 12.5 Before the process 4.49 0.48 0.20 0.098 1375 4.3 After the process 4.43 <0.01 0.153 0.010 1348 Ex. Comp. 3 12.8 Before the process 4.56 0.51 0.20 0.093 1369 5.1 After the process 3.60 <0.01 0.120 0.035 1345 Example 13 13.3 Before the process 4.51 0.56 0.21 0.098 1365 3.6 After the process 3.39 <0.01 0.180 0.011 1354 Example 14 11.9 Before the process 4.49 0.45 0.26 0.098 1371 2.9 After the process 3.39 <0.01 0.210 0.011 1352

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Petition 870180045283, of 05/28/2018, p. 49/60

45/46 [0099] As described above, by recycling the Mn contained in the secondary refining slag and the decarburization slag, the concentration of Mn in the molten pig iron after the desiliconization and dephosphorization process can be increased in comparison with the related technique. Therefore, even when steel products containing Mn according to the product specification are produced, the amount of an expensive Mn ore or Mn alloy used can be reduced.

[00100] Here above, preferred examples of the present invention have been described. However, the present invention is not limited to these examples. Additions, omissions, substitutions, and other modifications can be made to settings within a range without departing from the concepts of the present invention. The present invention is limited only to the scope of the accompanying claims without being limited to the above descriptions.

Industrial Applicability [00101] It is possible to provide a method of desiliconisation and dephosphorization of a cast pig in which a recycled slag generated in a cast steel stage is used to suppress a slag foam while reducing a total discharge amount slag in the molten steel stage; and as a result, overflowing can be efficiently prevented without increasing the capacity of the oven.

Brief Description of the Reference Symbols

1: Dephosphor furnace (Cast iron dephosphor furnace)

2: Top blow lance

3: Algarviz of base blowing

4: Oxygen gas tank

5: Nitrogen gas tank

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6: Base blowing tank (Fine powder base blowing tank)

7: Top blowing tank (Fine lime powder top blowing tank)

8: Feed hopper (Top feed hopper)

10: Decarburization furnace

11: Top blow lance

12: Oxygen gas tank

13: Base blowing gas tank

14: Algaraviz of base blowing

15: Feeder tank

P: Cast iron

S: Slag

PLD: Cast pig iron

Sld: Slag

Petition 870180045283, of 05/28/2018, p. 51/60

1/4

Claims (8)

1. Desiliconization and dephosphorization method of a cast pig iron, the method being characterized by the fact that it comprises: a process of blowing oxygen gas blowing an oxygen gas from a furnace top towards a surface of the molten pig iron; a process for adding recycled slag to supply at least one of a decarburization slag and a secondary refining slag towards the surface of the cast iron as a recycled slag; and a process for adding fine quicklime powder providing a fine quicklime powder having a maximum particle size of 500 μιτι or less at an ignition point in the molten pig iron, along with the oxygen gas blowing in towards the surface of the molten pig iron, in which the process of adding fine powder of quicklime starts at a starting time in which a concentration of silicon in the molten pig iron is reduced to 0% by weight or more and 0.15% by mass or less, further comprising a gas blowing agitation process to molten pig iron and agitation to molten pig iron with an agitation force ε within a range between 1.2 kW / t and 10 kW / t which is defined like the following Formula 1: 0.0062 xQ _f xT ^ε wl. ^x Jn ^] +] .54 1-í (Formula 1) where ε: a base blowing agitation force (W / t) applied to the pig iron Petition 870180045283, of 05/28/2018, p. 52/60 2/4 Qg: an amount of a base blowing gas (NL / minute; including a cracked gas from a solid material (for example, a fine limestone powder)) T: a temperature of molten pig iron (K) at the start of a base blow Tg: a temperature (K) of the base blowing gas before blowing H0: a depth of sofro (distance from a liquid surface of the molten pig iron to a tip end of a base blowing mesquite; (m)) Wm: a weight of the pig iron (including a scrap load; (t)). 2. Method for desiliconisation and dephosphorization of cast pig iron according to claim 1, characterized by the fact that the concentration of silicon in the cast iron at the start time is 0% by mass or more and 0.08% by mass or less. 3. Method for desiliconisation and dephosphorization of cast pig iron according to claim 1 or 2, characterized by the fact that in the process of adding recycled slag, when the concentration of silicon in the cast iron at the start of the addition process of recycled slag is less than 0.6% by mass, only secondary refining slag or both decarburization slag and secondary refining slag are supplied to pig iron, and when the concentration of silicon in pig iron in When starting the process of adding recycled slag, it is greater than or equal to 0.6% by mass, only the decarburization slag is supplied to the pig iron. 4. Iron desiliconization and dephosphorization method guPetição 870180045283, of 28/05/2018, p. 53/60 3/4 s cast according to any one of claims 1 to 3, characterized in that in the process of adding recycled slag, when the secondary refining slag is supplied towards the surface of the pig iron, a quantity of the slag secondary refining per 1 ton of cast iron is in the range between 0.1 kg and 16 kg. 5. Cast iron pig desiliconisation and dephosphorization method according to any of claims 1 to 4, characterized by the fact that it also comprises a process for adding a solid oxygen source to supply a solid oxygen source facing the surface of cast iron. 6. Cast pig iron desiliconisation and dephosphorization method according to any one of claims 1 to 5, characterized by the fact that it also comprises a process for adding a massive CaO source to supply a massive CaO source, which is derived of an ore having an average particle size of 5 mm or greater, facing the surface of the pig iron, where in the process of adding a massive CaO source, an amount of the massive CaO source per 1 ton of the pig iron is limited to be less than or equal to 7.5 kg. 7. Cast pig iron desiliconisation and dephosphorization method according to any of claims 1 to 6, characterized by the fact that a total amount of an MnO in the recycled slag is greater than 0% by weight and less than or equal to to 25% by mass. 8. Method for desiliconisation and dephosphorization of pig iron according to any one of claims 1 to 7, characterized by the fact that in the stirring process, a Petition 870180045283, of 05/28/2018, p. 54/60 4/4 fine limestone powder is supplied to the pig iron together with the blowing gas for the pig iron. Petition 870180045283, of 05/28/2018, p. 55/60 1/6 FTG. 1 2/6 3/6 ο , φ ο , φ .2? 2 .2 73 Ο .2 ^ro φ φ φ 73 Ο c ω μ = Ω_, φ 2 φ Ο.Τ3 ω σ & φ Ε ° 0.15% by weight or less Ο J * 05 05 <> = ΤΞ5 X σ σ— ο ω σ 8ο $ ^ro Ο 2 ω 0. σ ο ω ω φ ~ ο φ Q-O Ε ~ ω '5 ό ο ο C 105 ο t> Τ3 Ο 105 Ο Μ— »’ σ> ω σ ο ω ω ω ο ο ο ο 1 —- Ω_ C ο <φ ω σ> φ'χ σ ° ο ω ω φ ω φ -φ 8 ⁰⁵ Λ- Φ 0_ Ό ο φ φ σ Ο Q φ 73 ιφ Ο 73 .22 Φ £ Ξ Φ £ Φ Ο 73 ω ω φ ο ο ο CL 4/6