TW201435089A - Converter steelmaking method - Google Patents

Abstract

The present invention is capable of using a little of flux to increase efficiency of a desiliconization treatment and a dephosphorization treatment of a molten iron, decrease cost of fusion of a low phosphorus pig iron, and restrain cost of a decarbonization refinement. A converter steelmaking method of the present invention is: placing the molten iron in a first converter and performing the desiliconization treatment; slagging, and performing an intermediate slapping treatment to the rest of the slag and the molten iron remaining in the container; blowing an oxygen, a powder, a fuel gas, and a combustible gas from a lance and the like having a function of a burner to a bath level of the molten iron remaining in the converter after desiliconization, thereby performing the dephosphorization treatment of the molten iron; then, tapping the molten iron after dephosphorization, and allowing at least a part of a slag after the dephosphorization treatment to remain in the converter; and then, transferring the tapped molten iron after the depohosphorization treatment to other converter so as to perform the decarbonization refinement.

Description

Converter steelmaking

The present invention relates to a converter steelmaking method, and more particularly to a method of performing decarburization treatment and dephosphorization treatment while decarburizing and blowing a molten iron by a converter, and then performing steelmaking refining.

In the steelmaking method of recent years, before the decarburization refining of the converter, pretreatment of the molten iron in which the bismuth or phosphorus in the molten iron supplied from the blast furnace is removed in advance is usually performed. This molten iron pretreatment is carried out in accordance with the requirement of lowering the cost of the flux for refining or the like, increasing the purity of the molten steel, and improving the manganese yield in the converter and reducing the amount of refining slag by preventing peroxidation.

For example, in the case of the refining slag generated in the steelmaking step, there is a case where fluorine in the constituent component is a target of regulation. At this time, the method of pre-treating the molten iron without using fluorite (CaF ₂ ) which is a fluorine source is effective. In addition, in recent years, the demand for reducing the amount of greenhouse gas emission in the iron-making industry has been increased, and the use ratio of the blast furnace molten iron which requires a large amount of energy when reducing iron oxide is reduced, and on the other hand, the iron is required to be increased. A steelmaking method using a ratio of cold iron source such as chips. Under such circumstances, in recent steelmaking methods, there has been a tendency to improve the molten iron pretreatment method and increase the use ratio of the cold iron source.

However, in the pretreatment of the molten iron for demagnetization and/or dephosphorization, there is a method of using a converter type vessel, that is, a converter, as a gas to supply gas while adding a refining agent (flux) such as quicklime. Or a solid oxygen source such as iron oxide, and a furnace for removing bismuth or phosphorus in the molten iron in the slag. Since the converter uses a large amount of chips, it is advantageous to use a converter having a large furnace volume. In this respect, Patent Document 1 proposes a method in which a decarburization treatment is carried out using a converter type reaction vessel, and after the iron-slag discharge is performed, the demagnetized molten iron is again charged in the converter-type reaction vessel. In the pretreatment method for dephosphorization treatment, dephosphorization is performed efficiently by adjusting the concentration of ruthenium in the molten iron after the deodorization treatment or the alkalinity of the slag and the concentration of iron oxide without using fluorite.

Further, Patent Document 2 discloses the following method (double slag method): in the pretreatment method of continuously performing the demagnetization treatment and the dephosphorization treatment of the molten iron by the converter type container, the dephosphorization of the previous charge is performed. 40% by mass to 60% by mass of the treated slag remains in the container, and is used for deodorization and dephosphorization treatment, thereby reducing the amount of slag generated.

Patent Document 3 discloses a method in which a molten iron in a converter is subjected to a desulfurization treatment and a dephosphorization treatment using a converter, and in the converter, after the slag is removed after the deodorization treatment, dephosphorization is performed. deal with. In this method, it is possible to control the composition after the dephosphorization by controlling the composition in the manner described later, and to facilitate the subsequent dephosphorization treatment.

[Prior Art Literature]

[Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. 2002-129221

[Patent Document 2] Japanese Patent Laid-Open No. 2002-256325

[Patent Document 3] Japanese Patent Laid-Open No. 2001-271113

The method disclosed in Patent Document 1 performs dephosphorization treatment by performing iron removal and slag discharge from a converter type container after the deodorization treatment, and then de-phosphorizing the molten iron in the container again. The reduction in phosphorus concentration is advantageous. However, since this method requires repeated tapping and charging, there is a problem that productivity is remarkably poor when it is implemented by one converter type container. However, in this method, two converter type containers may be used for the molten iron pretreatment. However, at this time, there is a problem that a large amount of equipment costs are required, and heat loss due to heat release from the furnace body is increased. Further, in this method, there is also a problem that an increase in refining cost due to the necessity of adding a large amount of flux in the delining treatment and the dephosphorization treatment, and an increase in heat loss due to heat absorption of the flux. Further, in this method, in order to promote slag formation or increase the efficiency of the dephosphorization reaction during the dephosphorization treatment, iron oxide such as iron ore is introduced, and thus there is an endothermic or intermediate iron stagnation accompanying the decomposition reaction of the iron oxide. The problem of large heat loss. In addition, there is also the following problem: since the dephosphorization slag which does not use fluorite is relatively high in alkalinity, at the end of the dephosphorization treatment, the solid-phase ratio in the slag is also high and the fluidity is poor, and the droplets of the molten iron are mixed into the slag. The slag is discharged to the outside without being separated, resulting in an increase in the loss of the raw material metal. In addition, a part of the raw material metal can be recovered as a source of iron by magnetic separation, but the fine iron particles mixed in the slag cannot be recovered, so that most of the raw materials are used together with the slag in civil engineering. The treatment is carried out while the loss of the raw material metal is large.

Then, in Patent Document 2, it is proposed that the degassing treatment and the dephosphorization treatment are continuously performed by one converter type container, and only 40% by mass to 60% of the slag after the dephosphorization treatment is discharged. The mass %, and the remaining slag is used for the degreasing and dephosphorization treatment of the next feeding, thereby preliminarily reducing the amount of flux used and the amount of slag generated, and expecting a decrease in heat loss. However, in this document 2, not only the range of the appropriate slag composition or the treatment temperature in the delining and dephosphorization treatment, but also the dephosphorization treatment is performed in a state where a large amount of generated degreasing slag remains in the furnace. Therefore, a large amount of lime-based flux for adjusting the alkalinity of the slag is required in melting the low-phosphorus pig iron. Therefore, although the degreasing slag is not generated, the amount of dephosphorization slag in the furnace is increased and the reaction efficiency is lowered, and the amount of dephosphorization slag discharged is increased, so that the problem of loss of the raw material metal in the dephosphorization slag remains.

In the method of Patent Document 3, it is proposed that the slag remains in the furnace after dephosphorization of the molten iron, and the composition of the slag after the degassing and blowing of the next feeding is set to have a basicity of 0.9 to 1.1 and a slag (T.Fe). = 15% by mass to 20% by mass is discharged, thereby preventing the return of phosphorus in the fluffing and blowing, and reducing the unreacted lime in the slag. However, this method has a possibility of returning phosphorus due to fluctuations in the composition of the slag after the de-steaming. In particular, in the continuous operation, there is a problem that if the slag after the deodorization is not efficiently discharged out of the system, the phosphorus-containing slag remains, and due to the alkalinity of the slag or the slag (T.Fe) ) It is difficult to stabilize the dephosphorization reaction.

The main object of the present invention is to provide a converter steelmaking method capable of improving the efficiency of de-smelting treatment and dephosphorization treatment of molten iron with a small amount of flux, thereby reducing the melting cost of low-phosphorus pig iron and also suppressing decarburization. The cost of refining.

Further, another object of the present invention is to provide an effective converter for expanding the effective use of slag generated during melting and reducing the loss of raw material metal in the slag. Steel method.

For the above purpose, the inventors and the like have studied the following methods: in the steelmaking refining process of depurination, dephosphorization, and decarburization, even if the amount of the fluxing material is suppressed, the phosphorus concentration can be efficiently reduced, and at the same time Ensuring a heat source for scrap melting and increasing iron yield. As a result, it was found that desulfurization was further carried out in either or both of the deodorization treatment and the dephosphorization treatment in the molten iron pretreatment of the molten iron in the converter and the dephosphorization treatment of the molten iron. In the refining, if a burner-operated upper blow nozzle having a combustion hole (burner hole) capable of further supplying a fuel gas or a combustion-supporting gas in addition to the oxygen or powder outside the refining is used, The above object is easily achieved, thereby developing the present invention.

That is, the present invention is a converter steelmaking method in which a first converter is subjected to decarburization treatment and dephosphorization treatment in the decarburization refining of molten iron, and then decarburization refining is performed in a second converter to obtain a molten steel. The converter steelmaking method is characterized in that first, after the molten iron is placed in the first converter, the oxygen for refining and the powder containing the lime-based flux are blown from the nozzle to perform the disintegration treatment of the molten iron. Then, the slag is discharged from a part of the slag after the deodorization treatment, and the remaining slag and the molten iron remain in the middle of the slag discharge treatment; and then, the disintegrated molten iron remaining in the converter The bath surface, the oxygen for refining and the powder containing the lime-based fluxing material are blown from the nozzle to perform dephosphorization treatment of the molten iron; then, the molten iron after dephosphorization is subjected to iron removal, and the slag after dephosphorization treatment is performed At least a part of the molten iron remains in the converter, and then the molten iron after the dephosphorization treatment of the tapped iron is transferred to the second converter for decarburization refining to obtain a molten steel, and the blown refining is used. Oxygen, a powder containing a lime-based fluxing material, a fuel gas, and a burner having a burner function are subjected to either or both of the above-described deodorization treatment and the above dephosphorization treatment.

In the above method of the present invention, the following method is preferably employed.

(1) In the first converter, 30% by mass or more of the amount of slag after the dephosphorization treatment generated during the previous dephosphorization treatment is left, and then at least the untreated melt is placed in the first converter. Iron, and blowing the refining oxygen and the powder containing the lime-based fluxing material from the upper blowing nozzle or the nozzle having the burner function, or further blowing the fuel gas and the combustion-supporting gas, thereby performing the disintegration treatment of the molten iron Then, 40% by mass or more of the slag after the deodorization treatment is discharged to the intermediate slag discharged outside the furnace, and then the refining oxygen is blown by the first converter using the upper blowing nozzle or the nozzle having the burner function. a powder containing a lime-based fluxing material, or a fuel gas and a combustion-supporting gas, thereby performing dephosphorization treatment of the molten iron; (2) using the above-described nozzle having a burner function in decarburization refining; (3) The burner combustion heat supplied from the burner having the burner function used in the above-described dephosphorization treatment, the dephosphorization treatment, the decarburization refining, or the two or more treatments is 10 MJ/t or more. (4) Deodorization treatment, dephosphorization treatment The above-described burner-operated nozzle used in any one or two or more types of decarburization refining is a multi-tube nozzle having a refining oxygen passage, a powder supply passage, a fuel gas passage, and a combustion-supporting gas passage. (5) In addition to the fluxing material or the auxiliary material, the above powder is blown into the iron oxide material or the manganese oxide together with the carrier gas containing an inert gas such as argon or nitrogen. One or more; (6) The slag after the dephosphorization treatment is 60% by mass or more of the amount generated during the dephosphorization treatment, and remains in the converter.

(1) According to the converter steelmaking method of the present invention having the above-described configuration, the lime component in the slag after the dephosphorization treatment can be effectively used as the lime source in the deodorization treatment of the next feeding, and at this time, By suppressing rephosphorization in the dislocation treatment, the amount of the lime-based fluxing material used in the entire steelmaking process, particularly the molten iron pretreatment process, can be reduced.

(2) According to the present invention, in the molten iron pretreatment step, intermediate slag is discharged after the deodorization treatment, and then dephosphorization treatment is performed by the same converter, so that considerable heat dissipation due to conversion of the refining vessel can be performed. The heat is used as a heat source for melting the cold iron source, and the high-temperature dephosphorization-treated slag generated in the previous charge can be effectively used as a fluxing material. Therefore, if compared with the case of adding a fluxing material at normal temperature, the heat of heat absorption can be effectively used as heat for melting the cold iron source, and then the amount of use of the cold iron source (chip) can be increased, and further, it can be lowered. Loss of raw material metal.

(3) According to the present invention, in the molten iron pretreatment step, between the deodorization treatment and the dephosphorization treatment, the low alkalinity slag generated during the deodorization treatment is discharged outside the furnace, thereby maintaining a relatively high Since the basicity ((% by mass CaO/mass% SiO ₂ ) = 1.2 to 3.0), the amount of the lime-based fluxing material used in the dephosphorization treatment can be reduced.

(4) According to the present invention, an upper blowing oxygen nozzle (hereinafter, simply referred to as "a nozzle having a burner function") having a function of a burner for combustion which can be blown into a powder is used. It is easy to discharge the low alkalinity slag generated during the deodorization treatment outside the furnace, and the iron loss in the discharged slag can be reduced.

(5) According to the present invention, the powder supplied from the burner hole of the above-described nozzle having a burner function serves as a heat transfer medium, and can supply heat to the molten iron and the slag with high efficiency, thereby making up for the debris. The heat loss caused by the addition of the iron oxide source used as the dephosphorization agent, and the loss of iron particles in the slag.

(6) According to the present invention, when the powder supplied from the burner hole of the burner having the burner function becomes a heat transfer medium, the powder is heated, thereby contributing to the improvement of dephosphorization in the molten iron. In the blowing, the dephosphorization efficiency by the flux is promoted, the reduction of the Mn ore during decarburization refining is promoted, and the refining cost is lowered.

1‧‧‧ converter

2‧‧‧ nozzle

3‧‧‧ bottom blowing air outlet

4‧‧‧iron outlet

5‧‧‧Refining oxygen

6‧‧‧Combustible gas

7‧‧‧fuel gas

8‧‧‧ hopper

9‧‧‧ molten iron

10‧‧‧Deslag

11‧‧‧cold iron source

14‧‧‧Loading the pot

15‧‧‧ Resources

16‧‧‧Lime-based fluxing materials

17‧‧‧Dephosphorization slag

18‧‧‧ powder blowing path

19‧‧‧fuel gas pathway

20‧‧‧Combustible gas path

21‧‧‧Refining oxygen pathway

22a‧‧‧Cooling water access

22b‧‧‧Cooling water access

23‧‧‧ nozzle wafer

Fig. 1 is a schematic line diagram of a converter type container used in a pretreatment method.

Fig. 2 is a view showing the steps of the molten iron pretreatment method of the present invention.

Figure 3 is a cross-sectional view of a nozzle with a burner function.

Fig. 4 is a graph showing the relationship between the amount of heat supplied from a nozzle having a burner function and the slag discharge rate of the Si slag.

Fig. 5 is a graph showing the relationship between the amount of heat supplied from a nozzle having a burner function and [P] after P-blowing.

Fig. 6 is a graph showing the relationship between the amount of heat supplied from a nozzle having a burner function and the yield of Mn ore.

The preferred converter steelmaking method of the present invention is a method of pretreating molten iron using a converter and performing decarburization refining. As the converter, a top-blow converter (refining furnace) 1 as shown in Fig. 1 was used. Further, the present invention is characterized in that, when the molten iron in the converter 1 is subjected to either or both of the deodorization treatment and the dephosphorization treatment, the liftable burner function is described in detail below. The nozzle 2 can be blown into the front end of the upper blowing oxygen nozzle 2 having a function of a burner for combustion of various types of powder, and is blown to the bath surface (melted iron) by oxygen (upward blowing) for refining. Here, as the oxygen, it is preferred to use pure oxygen for industrial use. Further, the bottom blowing is performed using the bottom blowing tuyere 3 provided at the bottom of the converter 1. The bottom blowing gas is usually a gas containing oxygen or an inert gas such as argon (Ar) gas or nitrogen gas, or may have a stirring which strengthens the molten iron by blowing into the molten iron to promote melting of the cold iron source. The functional gas is further a gas having a function of blowing a fluxing material into the molten iron together with the gas for transport. Further, reference numeral 4 in the drawing is a tap hole for discharging the molten iron 9 after refining.

In carrying out the method of the present invention, for example, using at least two converters, at least one of the converters 1 is used for molten iron pretreatment, and at least one of the remaining at least one is used for decarburization refining of the pretreated molten iron to produce a melting. steel. That is, in the present invention, it is preferable to carry out pretreatment by the first converter for the molten iron pretreatment, and then transfer the pretreated molten iron to the second converter for decarburization refining for decarburization refining.

The nozzle 2 having the burner function characteristic of the present invention is as shown in the cross-sectional structure of Fig. 3. As described above, it is an upper blowing oxygen nozzle having a function of a burner for blowing into a powder. The nozzle 2 with a burner function has a concentric 6-tube structure, and the central passage is used for conveying an inert gas such as Ar or N ₂ as a conveying gas, and blowing lime powder or iron oxide powder, Mn ore powder, and the like. The powder blowing passage 18 of one or two or more kinds of powdery refining materials (powder) of the fluxing material has a plurality of annular passages on the outer side. The annular passage includes, in order from the inner side (inner tube), a fuel gas passage 19, a combustion-supporting gas passage 20 such as combustion oxygen or air disposed outside the fuel gas passage 19, and then disposed outside the combustion-supporting gas passage 20 The refining oxygen passage 21 and the outermost portion disposed outside the refining oxygen passage 21 are configured as a cooling water passage 22a and a cooling water passage 22b that circulate the inner and outer passages at the lower end. A nozzle wafer 23 made of a copper casting is attached to the lower end portion of the main body of the nozzle 2 by welding or the like.

In the present invention, the reason why the burner 2 having the burner function capable of supplying the refining powder as described above is used instead of the usual upper blowing oxygen nozzle is that the combustion of the burner can be efficiently performed. The heat is transferred to the molten iron, so that the heat required for the melting of the chips or the like can be efficiently supplied. Further, since the refining powder injected from the nozzle becomes a heat transfer medium for burning heat of the burner, and the refining powder itself is also added in a heated state, the slag temperature rises, and the slag discharge and the discharge after the dislocation step are promoted. The ratio of the molten iron suspended in the slag helps to reduce the lime as a flux and increase the yield of iron. Further, when the nozzle 2 having a burner function is used in the molten iron dephosphorization blowing, the melting of the lime source is promoted, so that the dephosphorization reaction is improved. Further, in the decarburization blowing, when the nozzle 2 is used, it contributes to an improvement in reaction efficiency such as reduction of Mn ore.

Hereinafter, according to FIG. 2, the use as a part of the converter steelmaking method of the present invention will be described. A method of pretreating the molten iron in the first converter 1 will be described. As shown in the figure, the molten iron pretreatment method comprises: sequentially performing (A) molten iron charging, (B) deodorizing treatment, (C) intermediate discharging, (D) dephosphorization treatment, (E) tapping. The step of refining the efficient molten iron can be achieved by performing the steps in the same converter, in particular in the same converter. Hereinafter, an example in which the above-described nozzle having a burner function is used in both the deodorization treatment and the dephosphorization treatment will be described. Of course, the nozzle with the burner function can also be used for any type of treatment.

(1) molten iron loading step (A)

In the step (A), in the converter (refining furnace) 1, at least the dephosphorization-treated slag (hereinafter simply referred to as "dephosphorization slag") 17 generated during the pretreatment of the previous molten iron is used. In a state where a part remains in the furnace, a new molten iron 9 is loaded from the charging pot 14, or a cold iron source 11 such as iron filings is placed before the molten iron is charged, and then the molten iron 9 is loaded. As the cold iron source 11 which is previously charged into the converter type refining furnace 1, in addition to the iron filings specified in the "Iron Standards for Iron Filing Inspection" of the Japan Iron Source Association, iron such as direct reduced iron or cold pig iron is used. Ingredients.

In the converter 1, the dephosphorization slag 17 generated in the previous refining (pre-feeding) which is provided in the next refining (next feeding) has the slag alkalinity at the time of the dislocation treatment for the next feeding. The role. In other words, the alkalinity (% by mass CaO/% by mass SiO ₂ ) (hereinafter, simply referred to as "basicity") of the dephosphorization slag is 1.2 or more, preferably 1.4 or more. The reason is that when the alkalinity of the previously added dephosphorization slag 17 is less than 1.2, even if the dephosphorization slag remains, the alkalinity adjustment in the deodorization treatment is insufficient, and a large amount of lime-based fluxing material needs to be added. In addition, the upper limit of the alkalinity is not particularly limited, and since the slag basicity in the usual molten iron dephosphorization treatment is about 3.0 or less, it is not necessary to increase the alkalinity to be higher than the above.

Further, in order to effectively adjust the alkalinity, the amount of the dephosphorization slag 17 remaining in the furnace is 30% by mass or more, preferably 60% by mass, based on the amount of the dephosphorization slag produced by the previous feeding. Above ~100% by mass. Further, if the total amount of the dephosphorization slag 17 previously charged in the furnace is effectively used for the deodorization treatment of the next feeding, the alkalinity adjustment in the deodorization treatment becomes easier. Further, if such a method is continued, the discharged pretreated slag becomes only the degreasing slag at the time of intermediate slag discharge, and does not discharge the dephosphorization slag having a high alkalinity, and therefore does not cause slag due to the hydration reaction. Problems such as swelling or dissolution of alkali. Therefore, the method of the present invention is also extremely effective in terms of seeking utilization of slag.

Further, since the dephosphorization slag 17 has a relatively high alkalinity and a low temperature (about 1350 ° C or less), the solid phase ratio is high and the fluidity is low. Therefore, in terms of the heat balance and the material balance, if the decarburization slag is left in the furnace in advance, there is no need for an inefficient operation such as adding a large amount of cooling material for curing. In addition, the dephosphorization slag 17 is rich in solid phase due to the above-described characteristics, and has low fluidity. Therefore, the structure contains a large amount of fine metallic iron, and the slag is pulverized and then subjected to magnetic separation treatment, and then contains about 10% by mass or more of metallic iron. . Previously, it was discharged as a slag out of the system, but according to the present invention, it was brought to the next feeding together with the slag, so that most of the metallic iron in the slag was recovered into the molten iron, and the loss of the iron source was reduced. Effect.

In addition, the slag at the end of the deodorization treatment (the slag after the deodorization treatment, hereinafter referred to as "debonding slag") has a high liquid phase ratio and a relatively high fluidity, so that it is in the slag. The metal iron component is easily separated, and the metal iron component remaining in the slag is not recovered after the pulverization of the slag and the magnetic separation treatment. Therefore, in the method of the present invention, the iron loss in the slag can be reduced by the entire molten iron pretreatment.

(2) Dislocation treatment step (B)

In the step (B), the converter 1 is erected, and the refining oxygen 5 is mainly sprayed from the nozzle 2 having the burner function and the like, and the refining oxygen is mainly blown off, and simultaneously blown as the combustion-supporting gas 6 The combustion oxygen is desorbed from the fuel gas 7 and the refining powder. In particular, the untwisting treatment step is characterized in that the source 15 contained in the hopper 8 and the refining powder containing the lime-based flux 16 are supplied from the center passage of the burner 2 having the burner function. 18. Performing an up-blowing jet in a combustion gas environment by a burner. Further, the powders may be supplied from chutes (not shown) as needed. At this time, the burner 2 having the burner function can be added by the burner function of the combustion-supporting gas 6 and the fuel gas 7 while adding the carbon material or the source of the heat source which is supplied from the center passage or becomes the oxygen source. Iron oxide, etc. From the viewpoint of melting a large amount of the cold iron source 11 as the oxygen source for the decarburization treatment, it is preferable not to use the iron oxide having a large heat absorption amount and the oxygen for refining from the nozzle 2 having the burner function. The passage 21 is only blown with oxygen 5.

In the dislocation treatment, the crucible or the crucible source 15 contained in the molten iron 9 and the crucible contained in the cold iron source 11 and transferred to the molten iron by melting are reacted with the oxygen source (Si + O ₂ → The SiO ₂ ) is desorbed, whereby the reaction efficiency of the subsequent dephosphorization treatment can be improved. At the time of the deuterium treatment, oxidizing heat is generated, and the molten iron temperature rises due to the heat of oxidation to promote melting of the cold iron source 11 in the molten iron.

Regarding the composition of the slag at the stage of the deuteration treatment, the amount of the dephosphorization slag 17 previously added in the furnace and the estimated value of the composition thereof, and the production of cerium oxide produced by the above reaction are considered. The slag basicity at the end of the decanting treatment is adjusted to be 0.5 or more and 1.5 or less. When the basicity is less than 0.5, the phosphorus is removed from the previously-added dephosphorization slag 17 remaining in the furnace, and the phosphorus concentration in the molten iron rises, and the dephosphorization load in the subsequent step becomes large and inefficient. Therefore, the alkalinity of the degreasing slag at the end of the decanting treatment is 0.5 or more, and more preferably 0.7 or more. In addition, when the alkalinity is higher than 1.5, the fluidity of the slag is lowered. Therefore, there is a problem that the amount of slag discharged during the subsequent intermediate slag removal is small or the amount of slag is difficult to be controlled, and the lime-based fluxing material is also inefficient. . Therefore, the slag basicity at the end of the decanting treatment is set to 1.5 or less, more preferably 1.2 or less. Further, in addition to the lime-based fluxing material such as quicklime or limestone or dolomite, a steelmaking slag selected from the group consisting of decarburization slag, dephosphorization slag, and ladle slag is used as a fluxing material.

The temperature of the molten iron at the end of the untwisting treatment is adjusted to be 1260 ° C or higher, 1450 ° C or lower, and more preferably 1400 ° C or lower. The reason is that if the molten iron temperature becomes higher than 1450 ° C, phosphorus is removed from the dephosphorization slag 17 remaining in the furnace, resulting in an increase in the phosphorus concentration in the molten iron, so that not only the dephosphorization load in the subsequent step is changed. Large and inefficient, and in order to prevent the loss of lining magnesia carbon bricks, it is also necessary to increase the concentration of magnesium oxide in the slag, resulting in high cost. On the other hand, when the molten iron temperature is less than 1260 ° C, the fluidity of the slag is lowered, the slag discharge amount at the time of intermediate slag discharge in the next step is small or the problem of slag discharge amount is difficult to be controlled, and the melting speed of the swarf is lowered. .

Further, in order to perform dephosphorization efficiently, the control of the molten iron temperature at this stage is also effective in the subsequent dephosphorization step. For example, when the temperature of the molten iron at the end of the degreasing treatment is 1350° C. or lower, the amount of the cooling material to be added such as iron ore added to adjust the temperature during the dephosphorization treatment can be greatly reduced. In the present invention, since the deodorization treatment and the dephosphorization treatment are continuously performed in the same converter, there is also a case where it is difficult to load the chips before the dephosphorization treatment in terms of work time. In addition, the cold iron source such as chips that can be supplied from the furnace during the treatment is limited in the amount of the particles whose particle size is adjusted, or the amount of the raw material metal generated in the ironworks is limited, so that it is difficult to stably use the product in large quantities. . Actually, there is a case where the number of types of auxiliary materials that can be used in the furnace is limited, and there is a case where the cold iron source cannot be supplied from the furnace. In short, the actual situation is that the cooling material used in the dephosphorization treatment step is limited to iron oxide such as iron ore, and it is not possible to sufficiently utilize a cold iron source such as inexpensive chips.

In the step of the dislocation treatment, it is relatively easy to increase the amount of the inexpensive chips, and therefore the temperature of the molten iron after the deodorization treatment can be set to 1400 ° C or lower. However, the melting rate of the chips is greatly affected by the temperature of the molten iron, and heat supply is substantially required. In addition, when the Si concentration of the molten iron is high, the alkalinity in the deodorization and blowing is adjusted only by the lime component remaining in the dephosphorization slag 17 in the furnace, which may be insufficient. In this case, in the present invention, a novel lime source such as decarburization slag may be added using the above-described nozzle 2 with a burner or a chute. This promotes the melting of the added lime source, but is effective for reducing the slag discharge property after the deodorization treatment and the iron particle loss in the slag discharge, and as a result, the use of the above-described burner-equipped oxygen supply nozzle 2 Improvements in this area are truly effective.

When the molten iron blending ratio is low, there is a case where the melting of the scraps remains, and if it is directly held together with the molten iron in the converter, it may be melted before the next dephosphorization treatment step. That is, with regard to the cold iron source, if the melting is completed by the end of the dephosphorization treatment, there is no problem in operation.

Further, the temperature of the molten iron after the deodorization treatment may be a value measured by a thermocouple or the like, or a calculated value based on the heat balance may be used. For example, as a calculation method based on the heat balance, the calculation can be performed according to the following formula (1), but is not necessarily limited thereto. There is a tendency to adjust the coefficient according to individual device conditions or operating conditions, or a slightly higher calculated value than adding or removing variables, but it is the degree of error.

T={0.21T _i . X _p -42.9X _s +(4137+0.327T _i )X _Si -746.6X _c -(575.5+0.025T _i )X _ore +(3239-0.115T _i )X _O2 +28.2X _f -1638W ^{-(1/ 3)} X _t }/(0.21X _p +0.179X _s +0.535X _Si +0.468X _C +0.151X _ore +0.115X _O2 +0.241X _f )-(1)

T: molten iron temperature after deodorization treatment (°C)

T _i : temperature of the molten iron (°C)

X _p : basic unit of molten iron (kg/t) (the total weight of the molten iron and the weight of the cold iron source is the same per 1t, the same below)

X _s : basic unit of cold iron source (kg/t)

X _Si : the basic unit of the oxide (kg/t)

X _C : basic unit of carbon in the additive (kg/t)

X _ore : basic unit of iron oxide (kg/t)

X _O2 : basic unit of gas oxygen (Nm ³ /t)

X _f : basic unit of fluxing material (kg/t)

W: converter molten iron capacity (t)

X _t : time from the last feeding of the tap to the end of the dislocation process (minutes)

The cerium (X _Si ) which is an oxide in the above formula (1) is a total of those contained in a molten iron or a cold iron source, an additive or the like. Among them, the cerium concentration in the molten iron uses the rapid analysis value of the sample collected from the molten iron before each charging. However, it is also possible to use a method in which calculation is performed using another analysis value such as a tapping component of a blast furnace. Further, the concentration of ruthenium in various cold iron sources can be, for example, an analysis value of a representative sample per batch, but in many cases, cold pig iron is stable at a concentration equivalent to that of molten iron. In addition, although the cerium concentration in the swarf is fluctuated by the source, it is stable at a concentration of about 1/10 or less of the pig iron. Therefore, it can be used as a representative value or can be ignored.

Non-oxide ruthenium is present in the above additives. This refers to the inclusion of bismuth telluride or ruthenium metal, tantalum carbide, tantalum nitride or other ruthenium compounds. As a representative additive, in addition to ferro-silicon, it will be mentioned that it will contain about 60 masses. The powder of % of niobium carbide is molded into a briquettte (hereinafter referred to as a niobium carbide crucible).

As a method for analyzing non-oxide ruthenium in the additive, in addition to the analysis method of ferroniobium described in JIS G 1312, full enthalpy analysis, acid soluble enthalpy analysis, all carbon analysis, total oxygen analysis, and total Nitrogen analysis, thermal mass analysis, carbon analysis by a combustion method in which a temperature history is adjusted, analysis of other elements, analysis of a compound by an X-ray diffraction method, and the like are combined.

Moreover, carbon is additionally present in the additive. As the carbon source, carbon other than the carbon material such as coke or earthy graphite can be used. Further, as the fluxing material in the additive, an auxiliary material such as quicklime or light burned dolomite or magnesia clinker may be used, and dephosphorization slag, decarburization slag, pouring slag, etc. may be used. The slag serves as a source of calcium oxide or a source of magnesium oxide. Further, as an example of an inexpensive auxiliary material, a carbon oxide or a hydroxide of calcium or magnesium can be used. However, since the amount of heat absorption is large, it is preferably corrected in comparison with other fluxing materials when used in a large amount. The above formula (1).

As described above, in the untwisting treatment of the present invention, since the temperature of the molten iron after the treatment is controlled to an appropriate range and ruthenium is used as the heat source, the total unit weight of the molten iron and the cold iron source is 100 kg/t to 300 kg. A large amount of cold iron source of /t does not lead to a decrease in productivity or an increase in refining cost, and the melting of the cold iron source and the pretreatment refining of the molten iron can be efficiently performed. However, when the basic unit of the cold iron source is 300 kg/t or more, there is a problem that the heat source is further required to cause an increase in cost, or the blowing time becomes long and the productivity is lowered. In addition, due to the constraints imposed on the cold iron source loading device, further increase in usage is inefficient.

Although it is described in detail below, in order to improve the slag discharge property of the slag after the deodorization treatment, that is, the slag removal property 10, it is preferable to appropriately foam the slag in the molten iron pretreatment converter 1. Therefore, it is effective to increase the rate of generation of CO gas generated by the reaction of carbon in the molten iron with iron oxide in the slag. Therefore, in order to obtain a stable slagging rate in the next slag step, it is preferred to supply oxygen of a stoichiometric amount or more required for oxidation of ruthenium in the molten iron and the added ruthenium source.

The basic unit supplying oxygen to the molten iron in the silicon removal process, in addition to the amount of removed silicon stoichiometrically required, preferably set 2Nm ³ / t or more, desirably 4Nm ³ / t or more. In the present invention, the concentration of ruthenium in the molten iron at the time of completion of the devolatilization treatment is 0.1% by mass or less, preferably 0.05% by mass or less. Thereby, the slag discharge state can be maintained while the slag is discharged after the mashing treatment, and the slag discharge property can be favorably maintained, and the phosphorus return from the slag to the molten iron can be suppressed. According to the study by the inventors and others, it was confirmed that the oxygen supply rate of the nozzle 2 with the burner function described above was 1 Nm ³ /min. t~3Nm ³ /min. t, the bottom blowing gas blowing speed is 0.1Nm ³ /min. t~0.6Nm ³ /min. In the range of t, the above effects can be obtained. In addition, in order to determine the completion of the dislocation treatment, it is preferable to perform the slag discharge due to the decarburization reaction as described above, and it is preferable to determine the concentration of the exhaust gas during the deodorization and the CO and CO in the exhaust gas while monitoring. Decarburization rate calculated from ₂ concentration, exhaust flow rate, and exhaust gas analysis value.

(3) Intermediate slag removal step (C)

In the present invention, at the time of pretreatment of the molten iron, the slag discharging step of the slag is provided after the above-described deodorization treatment. In the slagging step (C), the low alkalinity degreasing slag containing a large amount of SiO ₂ generated during the decanting treatment is discharged from the converter 1. The so-called discharge slag 10 is effective in obtaining the appropriate slag alkalinity and reducing the amount of the lime-based flux to be used in the dephosphorization treatment in the next step. In addition, in the state in which a large amount of the previously-added dephosphorization slag 17 remains in the furnace, the pretreatment method of the molten iron by the next feeding is performed, since the self-slag is prevented from being melted. The dephosphorization treatment is carried out in the form of phosphorus back in the iron, and therefore, the concentration of phosphoric acid in the degumming slag is higher than before. Therefore, when a large amount of the slag is left in the converter 1, since the amount of phosphoric acid in the slag in the furnace in the next dephosphorization treatment step becomes excessively large and the dephosphorization effect is lowered, this step is prevented. The role of C) is also important. Further, the intermediate slag after the completion of the untwisting and blowing may cause the converter to be inclined, discharged from the furnace mouth, or may be carried out from the tap hole 4 of the molten iron.

In the converter steelmaking method of the present invention, in particular, in the molten iron pretreatment method of the first converter 1, since the processes of the steps (A) to (C) are continuously carried out repeatedly, if the discharge of the slag is not performed When it is sufficient, phosphoric acid accumulates in the furnace, so care needs to be taken. The reason is that if the amount of phosphoric acid in the slag in the furnace is excessive in the dephosphorization treatment stage, the dephosphorization reaction efficiency is lowered by the increase in the phosphoric acid concentration in the slag, and the phosphorus concentration in the molten iron after the treatment is increased, or The problem of an increase in the amount of use of the lime-based fluxing material required for the dephosphorization reaction.

Therefore, in the present invention, in order to solve this problem, the above-described nozzle 2 having a burner function is used. An example of preferable conditions of the dislocation treatment of the present invention is shown in Table 1, and the effects thereof are shown in Fig. 4 . According to Table 1 and FIG. 4, by using the nozzle 2 having a burner function, efficient heat supply to the molten iron and the slag can be achieved, and melting of the melt, lime, and iron oxide source can be achieved. The intermediate slag removal rate caused by the slag melting is stabilized at a high level, and the iron granules in the intermediate slag are reduced.

That is, in the same de-blowning condition, instead of the method of charging the refining agent according to the prior method, as in the present invention, if a nozzle 2 having a burner function is used, it is added as the refining agent for deodorization. The powder can be heated before the powder for refining or the like to be added to the bath surface, so that the melting of the slag is more efficient. That is, as shown in FIG. 4, focusing on the middle slag discharge, with a burner function When the nozzle 2 is supplied with heat of 10 MJ/t or more, the slag discharge rate of the slag is drastically improved. In addition, the ratio of the iron particles suspended in the slag was observed, and as a result, it was 10 mass% in the case of a normal burner or an upper blowing nozzle, but the heat of combustion by the burner was 10 MJ/ When the nozzle 2 having a burner function of t or more is reduced to 6 mass%.

In addition, when almost all of the degreasing slag generated during the deodorization treatment is subjected to slag discharge, the slag formation of the newly added lime-based flux in the dephosphorization treatment in the next step is slow, and becomes a hindrance factor of the dephosphorization reaction. . For this problem, fluorite may be added to promote slag formation, but if so, as described above, the use of the generated slag is restricted and difficult. To carry out the treatment of the slag. In addition, there is a method of adding iron oxide such as iron ore to promote slag formation. However, in this method, heat loss due to decomposition and endothermic reaction of iron oxide is large, and heat for melting of the cold iron source is reduced. Therefore it is not the best policy.

Therefore, the slagging rate in the intermediate slagging step is dealt with as follows. In other words, the slagging rate (% by mass) of the slag (the mass of the discharged slag) × 100 / (the mass of all the slag in the furnace at the end of the devolatilization treatment) is preferably at least 40% or more, preferably 60% or more. . The reason for this is that when the slag discharge rate is less than 40% by mass, as described above, the amount of the lime-based fluxing material used in the dephosphorization treatment in the next step is increased. In addition, when the amount of residual slag is increased, scum foaming cannot be suppressed, and slag discharge from the furnace mouth occurs during the dephosphorization treatment, which may cause an operation failure due to slag discharge.

In the present invention, the alkalinity of the slag at the end of the devolatilization treatment is in the range of 0.5 to 1.5, and the molten iron temperature at the end of the devolatilization treatment step is 1260 ° C or higher and 1350 ° C or lower to make the oxygen basic unit suitability. It promotes slag foaming. Thereby, good fluidity and gas holdup of the slag can be ensured, and good slagging can be performed only by sloping the slag from the furnace mouth by tilting the furnace body after the completion of the devolatilization treatment. In this respect, when the slag is discharged by adjusting the inclination angle of the furnace body so that the molten iron does not flow out, a certain amount of slag has to remain in the furnace, but the foamed slag is compared with the true specific gravity. The volume specific gravity is lowered, so that the amount of slag remaining in the furnace can be controlled to a low level.

(4) Dephosphorization treatment step (D)

After the slag removal step (C), the molten iron remaining in the same converter 1 is supplied with a powder and an oxygen source containing a lime-based flux as a re-concentrating agent for dephosphorization, and the molten iron is subjected to dephosphorization treatment. In terms of reducing heat loss, it is preferred that the oxygen source used in the dephosphorization treatment step only use oxygen 5 from the above-described upper blow nozzle 2 with a burner function. Phosphorus in the molten iron is oxidized to phosphorus oxide (P ₂ O ₅ ) by oxygen in the supplied oxygen source, and the phosphorus oxide is stably incorporated into the slag by the lime-based flux. In the slag, dephosphorization of the molten iron is performed. In order to carry out the dephosphorization reaction with high efficiency, it is preferred to use the above-described burner-equipped spray so that the alkalinity of the slag after the dephosphorization treatment (the dephosphorization slag 17 of the present feed) is 1.2 or more and 3.0 or less. The tube 2 or the shot is blown or fed into the lime-based fluxing material, and the dephosphorization treatment is performed so that the molten iron temperature after completion of the dephosphorization treatment by oxygen supply is 1280 ° C or more and 1360 ° C or less.

The reason for this is that when the slag basicity of the present dephosphorization slag 17 produced during the dephosphorization treatment is less than 1.2 or the molten iron temperature exceeds 1360 ° C, the dephosphorization ability of the slag is lowered, and the treatment cannot be sufficiently reduced. Phosphorus concentration in the molten iron. On the other hand, when the slag basicity exceeds 3.0, it is difficult to achieve slag formation of the lime-based flux, and the cost of the lime-based flux increases. When the molten iron temperature is less than 1280 ° C, it is still difficult to achieve slag formation of the lime-based flux. And the heat in the subsequent steps of decarburization refining is insufficient. In addition, in order to sufficiently ensure the heat during decarburization refining by another converter, it is preferable to set the molten iron temperature after completion of the dephosphorization treatment to 1280° C. or higher and 1360° C. or lower, and dephosphorization. The amount of oxygen used and/or the amount of carbon added in the deodorization treatment and the dephosphorization treatment are adjusted so that the carbon concentration in the molten iron at the end of the treatment is 2.5% by mass or more.

In the dephosphorization step (D), the effect of applying the nozzle 2 having the burner function is as shown in FIG. That is, in the nozzle 2 having a burner function, the dephosphorization agent itself is heated while the dephosphorization agent powder such as lime or iron oxide becomes a heat transfer medium for combustion of the burner, and the dephosphorization agent is promoted. The substance of the component moves, so that the dephosphorization efficiency becomes high. This can be understood by the following method as shown in FIG. 5, when the heat is supplied to the burner through the nozzle 2 with the burner function, and the heat of the burner is 10 MJ/t, the treatment is performed with respect to the same basic unit of lime. After [P] is stabilized at a low level.

(5) Ironing step (E)

In the step (E), when the phosphorus concentration in the molten iron is lowered to a specific value after the dephosphorization step (D), the converter 1 is tilted toward the side where the tap hole is provided, and the converter type is refined. The molten iron in the furnace is discharged to a molten iron holding container (not shown).

(6) Decarbonization refining

The dephosphorization molten iron of the first converter 1 is subjected to the pretreatment of the molten iron of the first converter 1 including the above steps (A) to (E), and then the converter for decarburization refining, which is the second converter, is used. The converter is subjected to decarburization refining to purify the specific molten steel. In this step, since the decarburization treatment is carried out using the dephosphorized molten iron, and the end point carbon concentration is not required to be lowered, the FeO formation in the terminal slag is promoted to improve the dephosphorization, and thus it is advantageous, for example, for Mn ore reduction. However, it is necessary to compensate for the reduction heat for the reduction of Mn ore and to improve the reduction efficiency of Mn ore. In this respect, if the above-described nozzle 2 having a burner function is used under the conditions shown in Table 3, it is effective as shown in Fig. 6. That is, as shown in Fig. 6, in the converter for decarburization refining, when the Mn ore is reduced, the nozzle 2 or the chute having the burner function is mainly used, and the heat supply amount from the burner is 10 MJ/t or more. The method of blowing or inputting heat to the Mn ore can thereby achieve thermal compensation in the reduction of the Mn ore, and at the same time, the reduction efficiency is also improved, and the Mn yield is improved.

As described above, in the converter steelmaking method in which the pretreatment of the molten iron and the decarburization refining are carried out using a converter, the following treatment is performed, that is, dephosphorization treatment of the molten iron. After the end, the iron is discharged, and then remains in the furnace without discharging at least a part of the slag after the dephosphorization treatment, and a new molten iron is charged therein for deodorization treatment, so that the result is a converter type refining furnace (pretreatment furnace) The slag discharged is mostly deodorized. Thus, the alkalinity of the degreasing slag is relatively low, and the mixing of the raw material metal is also small, so that there is no problem of swelling due to alkali elution or hydration reaction. In particular, in the method in which the dephosphorization slag is not completely discharged, in order to prevent such a problem at all, the treatment of the slag can be simplified, and it can also be applied to a high value-added application. In order to achieve efficiency and stabilization of processes having such characteristics, In the present invention, an upper blow nozzle having a burner function is used, and an increase in the slag discharge rate after the detachment and a decrease in the iron granules in the slag can be achieved.

[Example 1]

Using a converter 1 having a capacity of 300 tons as shown in Fig. 1, first, pretreatment of the molten iron was carried out. At the time of this treatment, the nozzle 2 with the burner function shown in FIG. 3 is used, and the oxygen for refining is blown to the bath surface (melted iron), and the eight bottom blowing tuyes provided at the bottom of the furnace body are in the molten iron. Blow in nitrogen for stirring. However, when the burner nozzle is not used, the four-tube nozzle of the fuel-free gas passage 19 and the combustion-supporting gas passage in Fig. 3 is used. In addition, the conditions of decarburization, dephosphorization, and decarburization of the decarburization converter for the pretreatment of the molten iron are shown in Tables 1 to 3, and the molten iron components are shown in Table 4-1. Table 4-3. Further, as a result of the implementation, the results of the desiliconization and blowing were shown in Table 4-1, the results of the de-P blowing were shown in Table 4-2, and the results of the de-C blowing were shown in Tables 4 to 3. These embodiments are examples in which a part or all of the slag after dephosphorization treatment by the dephosphorization treatment of the molten iron as the previous step is left in the furnace, and the inside of the converter is first charged with cold. The iron source, and then the molten iron is placed in the furnace, and then the refining oxygen is blown from the nozzle 2 having the burner function, and then the desulfurization is started, and then the intermediate slag is discharged, and then the same converter is used. Dephosphorization and then decarburization by another converter. Further, regarding the alkalinity compensation of the slag generated in the above-described deodorization treatment, the bulk lime is added from the input chute as needed, or the powder blowing passage 18 from the nozzle 2 having the burner function is in the burner. Add powdered lime under combustion. Further, the end of the blow-off blowing (treatment) in the molten iron pretreatment stage is determined by the change in the exhaust gas temperature and the CO concentration in the exhaust gas. Middle row in the table The slag rate was evaluated by weighing the slag pot.

According to Tables 4-1 to 4-3 which are shown as Comparative Example 1 and Inventive Example 1 to Invention Example 9, it is understood that neither of the two treatments is used during the deodorization blowing and the dephosphorization blowing. In the example of the nozzle having the burner function (Comparative Example 1), the intermediate slag discharge rate was poor, and the P concentration after the P removal was also high. Further, a nozzle having a burner function is used in the deodorization blowing, and on the other hand, the nozzle having the burner function is not used in the dephosphorization blowing (Inventive Example 1 to Inventive Example 3) In the middle, the P concentration after the P removal was slightly higher, but the intermediate slag removal rate was improved with respect to Comparative Example 1 in which the nozzle having no burner function was used during the deodorization blowing. Further, although sufficient heat is added from the nozzle having the burner function during the de-blown blowing, the nozzle having the burner function is not used in the dephosphorization blowing (Example 2, Inventive Example) In 3), the intermediate slagging rate is further improved. Therefore, it is understood that a nozzle having a burner function is preferably used at least in the stage of deodorization and blowing.

In addition, when the nozzle having the burner function is used at the time of deodorization and dephosphorization, and the heat input is adjusted to 10 MJ/t or more, the intermediate slag rate and the phosphorus concentration are ideal. The results (Inventive Example 4 to Inventive Example 9). Further, it was also found that when the nozzle having the burner function was used in the decarburization blowing under the same conditions, the Mn yield was improved (Inventive Example 8 and Inventive Example 9). In particular, it can be seen that if the nozzle having the burner function is used in all the steps of decarburization, dephosphorization, and decarburization, any aspect of the intermediate slagging rate, the CaO basic unit, and the Mn yield can be obtained. Both are ideal results.

[Embodiment 2]

This example is an example showing the result of investigating the influence of the residual ratio of the dephosphorization slag at the time of deodorization and blowing. Further, in this embodiment, the converter, the burner, and the like used are the same as those in the first embodiment, and the conditions of the blowing are also basically performed under the same conditions as those in the first embodiment, but only the dephosphorization residue is used. Operating conditions in which the residual rate is changed. Further, the results are shown in Table 5-1 to Table 5-3.

As is clear from the results shown in Table 5-1, according to Inventive Example 10 to Inventive Example 15, when compared with Comparative Example 2, the next addition of a part (50% to 100%) of the remaining dephosphorization residue In the untwisting and blowing, the intermediate slag removal rate or the CaO addition amount is reduced. Further, as is clear from the results shown in Table 5-2, the inventive examples 10 to 15 and the comparative examples 2 were not significantly different. Further, as shown in Table 5-3, in the series of treatments of deodorization blowing, dephosphorization blowing, and decarburization refining, the total Fe yield and the total CaO basic unit were increased.

[Industrial availability]

Although the present invention relates to a steelmaking method of a converter, it is of course also effective as a so-called pretreatment technique for molten iron.

1‧‧‧ converter

2‧‧‧ nozzle

3‧‧‧ bottom blowing air outlet

4‧‧‧iron outlet

5‧‧‧Refining oxygen

6‧‧‧Combustible gas

7‧‧‧fuel gas

8‧‧‧ hopper

9‧‧‧ molten iron

10‧‧‧Deslag

15‧‧‧ Resources

16‧‧‧Lime-based fluxing materials

Claims (7)

A converter steelmaking method, which is subjected to decarburization treatment and dephosphorization treatment in the first converter at the same time as decarburization refining of molten iron, and then decarburization and refining by a second converter to produce molten steel, the above-mentioned converter steelmaking The method is characterized in that first, after the molten iron is placed in the first converter, the refining oxygen and the powder containing the lime-based flux are blown from the nozzle to perform the disintegration treatment of the molten iron; a part of the slag is discharged after the deodorization treatment, and the remaining slag and the molten iron remain in the intermediate slag in the container; and then, the bath surface of the molten iron remaining in the converter is removed And blowing the above-mentioned refining oxygen and the powder containing the lime-based fluxing material from the nozzle to perform dephosphorization treatment of the molten iron; and then, the dephosphorized molten iron is subjected to iron removal, and after dephosphorization treatment At least a part of the slag remains in the converter; and after the molten iron after the dephosphorization treatment of the produced iron is transferred to the second converter to perform decarburization refining to obtain molten steel, the refining oxygen can be blown, and the above-mentioned inclusion Lime line One or both of the above-described deodorization treatment and the above dephosphorization treatment are performed on the nozzles having the burner function of the powder, the fuel gas and the combustion-supporting gas. The converter steelmaking method according to the first aspect of the invention, wherein the amount of the dephosphorization-treated slag remaining in the amount of 30% by mass or more generated in the first dephosphorization treatment in the first converter is followed by 1 at least the untreated molten iron is placed in the converter, and the above-mentioned refining oxygen is blown from the upper blowing nozzle or the nozzle having the burner function and the above The powder containing the lime-based fluxing material or the fuel gas and the combustion-supporting gas are further blown to perform the disintegration treatment of the molten iron, and then 40% by mass or more of the slag after the deodorization treatment is discharged outside the furnace Then, the slag is discharged in the middle; and the above-mentioned upper blowing nozzle or a nozzle having a burner function is used to blow the refining oxygen and the powder containing the lime-based flux, or to blow the fuel. The gas and the above-mentioned combustion-supporting gas are subjected to dephosphorization treatment of the molten iron. The converter steelmaking method according to claim 1 or 2, wherein the above-described nozzle having a burner function is used in the above decarburization refining. The converter steelmaking method according to any one of the above-mentioned claims, wherein the dephosphorization treatment, the dephosphorization treatment, the decarburization refining, or the two or more treatments are performed. The combustion heat of the burner supplied from the above-mentioned nozzle having a burner function is set to 10 MJ/t or more. The converter steelmaking method according to any one of the preceding claims, wherein the desulfurization treatment, the dephosphorization treatment, and the decarburization refining are used in one or more of the treatments The above-described nozzle having a burner function is a multi-tube nozzle having a refining oxygen passage, a powder supply passage, a fuel gas passage, and a combustion-supporting gas passage. The converter steelmaking method according to any one of claims 1 to 5, wherein the powder is transported with an inert gas such as argon or nitrogen in addition to the above-mentioned fluxing material or auxiliary material. Gas is blown into the iron oxide material or manganese oxide together Any one or more. The converter steelmaking method according to any one of the preceding claims, wherein the slag after the dephosphorization treatment is 60% by mass or more of the amount of the dephosphorization treatment remaining in the converter. .