KR20150095890A - Converter steelmaking process - Google Patents

Abstract

(Problem to be Solved) The use of a small amount of scavenger improves the efficiency of degassing and removing the molten iron, reducing the solvent cost of the low phosphorus pig iron, and reducing the cost of decarburization refining.
The present invention relates to a process for desulfurizing a furnace in which a molten iron is charged into a first converter to carry out degassing treatment and then a part of the slag is discharged after the degassing treatment and the remainder is left in the vessel together with the molten iron, treatment is performed on the bath surface of the molten iron after the degassing is performed in the furnace, and a refining oxygen, a powder containing the lime-keeping solvent, and further a fuel gas, such as a fuel gas, The molten iron is subjected to a deodorization process by injecting a delayed (flameproof) gas, and then the molten iron after the deodorization is tapped and at least a part of the slag is left in the converter after the dephosphorization process, The post charter line is transferred to the other converter, and decalcification is performed.

Description

CONVERTER STEELMAKING PROCESS

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a converter steelmaking method, and more particularly, to a method of manufacturing a converter by performing a desiliconization treatment and a dephosphorization treatment together with a decarburization treatment in molten iron, .

[0004] In recent steelmaking methods, it is common to perform a preliminary ironing treatment for removing silicon or phosphorus in a molten iron supplied from a blast furnace in advance prior to decarburization refining by a converter. The preliminary treatment of the molten iron is carried out in accordance with a request such as reduction of cost of flux for refining, high purity of molten steel, improvement of manganese yield by prevention of peroxidation in converter, reduction of refining slag amount and the like.

For example, in the case of refining slag generated in a steelmaking process, fluorine in constituent components may be subject to legal regulations. In this case, a method of pretreatment of molten iron without using fluorite (CaF ₂ ) as a fluorine source is effective. In recent years, there has been a growing demand for reduction in the emission of greenhouse gases to the iron and steel industry, and the use ratio of the furnace charcoal which requires a large energy to reduce iron oxide is reduced, There is also a request for a steelmaking method that increases the use of iron sources. Under these circumstances, in recent steelmaking laws, there is a tendency to increase the use ratio of cold iron sources while improving the pre-treatment method of iron wire.

In the pretreatment of molten iron pre-treatment for demolishing and / or removing the molten iron, a refining agent such as burnt lime (flux solvent) is added and a solid oxygen source such as gaseous oxygen or iron oxide is supplied, As a furnace for removing phosphorus in slag, there is a method using a converter type vessel, that is, a converter. This is because, in order to use a large amount of scrap, it is advantageous to use a converter having a large furnace volume. In this regard, Patent Document 1 discloses a method of removing contaminants by degassing using a converter type reaction vessel, tapping, slag removal, and degassing the reaction vessel again In a preliminary treatment method for carrying out a dephosphorization treatment by charging a molten iron, a method of effectively removing the fluorophosphate without using fluorite is proposed by adjusting the silicon concentration, the basicity of the slag and the iron oxide concentration in the molten iron after the degreasing treatment.

Further, Patent Document 2 discloses a preliminary treatment method for continuously carrying out a degassing treatment and a demineralizing treatment of a molten iron in a converter type vessel, wherein 40 to 60 mass% of the slag after the pretreatment of the charge is charged into the vessel (Double slag method) is disclosed in which the amount of slag generated is reduced by utilizing the residual slag and removing the slag and using it for degassing and denitrification.

Patent Document 3 discloses a method for refining molten iron by a converter in which a degassing treatment and a denitration treatment are carried out by using a converter, followed by the intermediate disposal after the degassing treatment in the converter, followed by the denitration treatment. According to this method, it is possible to control the rephosphorization after detachment and to facilitate the subsequent de-phosphor processing through control of the composition as described later.

Japanese Patent Application Laid-Open No. 2002-129221 Japanese Laid-Open Patent Publication No. 2002-256325 Japanese Patent Application Laid-Open No. 2001-271113

The method disclosed in Patent Document 1 is advantageous for reducing the phosphorus concentration in the molten iron since the degumming treatment is carried out by charging the molten iron into the container again after tapping and dispensing from the converter container after the degasification treatment. However, since this method needs to repeat the outgoing and charging, there is a problem that the productivity is significantly lowered when it is carried out in one converter type container. However, in this method, two converter-type vessels may be used for the charcoal pretreatment. However, in this case, a high facility cost is required, and there is a problem that heat loss due to heat radiation from the furnace body is increased. Further, in this method, since it is necessary to add a large amount of a magic agent in the denitrification treatment and the denitrification treatment, the cost of refining is increased, and the heat loss due to endothermic absorption of the magic powder is also increased. Further, in this method, since iron oxide such as iron ore is injected in order to accelerate slag formation or improve the efficiency of the dephosphorization reaction at the time of the denitrification treatment, heat absorption due to the iron oxide decomposition reaction or heat Ross has a big problem. In addition, since the alkaline slag which does not use fluorspar has a relatively high basicity, the solid phase ratio in the slag is high at the end of the removal treatment and the fluidity is poor, and the droplets of the molten iron are mixed in the slag, There is also the problem of causing an increase in iron matrix loss. In addition, a part of the slag can be recovered as an iron source by grinding the slag and then magnetic separation. However, since most of the fine iron particles incorporated in the slag can not be recovered, It is disposable together with civil engineering use together, and the present loss is large.

Next, in Patent Document 2, in a single converter type vessel, the degassing treatment and the denitration treatment are continuously performed, and only 40 to 60 mass% of the slag is removed after the denitration treatment, , And is used in the dephosphorization treatment, a preliminary treatment method for reducing the consumption amount of slag agent and the slag generation amount is proposed, and reduction of thermal loss can be expected. However, this Document 2 does not disclose the proper slag composition and the range of the treatment temperature in the denitrification and dephosphorization treatment, but also the fact that the dephosphorization treatment is carried out while the undegraded slag produced in a large amount remains in the furnace Solventing of low-phosphorus pig iron requires a large amount of lime-based polishing agent to adjust the slag basicity. As a result, no demagnetizing slag is generated, but the amount of demagnetizing slag in the furnace is increased to lower the reaction efficiency, and the amount of demagnetizing slag discharged is rather increased, so that the problem of the present loss in the demagnetizing slag has been left.

With respect to the method of Patent Document 3, the slag is left in the furnace after the charcoal removal, and the slag composition after the next charge removal is discharged as 0.9 to 1.1 in basicity and 15 to 20% by mass in slag as T. Fe, Thereby preventing blooming and reducing unreacted lime in the slag. However, in this method, there is a possibility that blooming may occur due to fluctuation of the slag composition after bleaching. Particularly, in the case of continuously operating the slag, the slag containing phosphorus remains, unless the slag after the removal of the flue gas is efficiently discharged to the outside of the system, so that the slag of the slag and the slag (T.Fe) There is a problem that it is difficult to stably advance the denitration reaction.

The main object of the present invention is to propose a transformer steelmaking method capable of increasing the efficiency of degassing and demining of a molten iron with a small amount of scouring agent, reducing the solvent cost of the low iron wire, and suppressing the cost of decarburization refining.

It is another object of the present invention to propose effective transfer steelmaking processes which are effective for increasing the effective utilization of slag generated in the application and for reducing the present loss in slag.

In view of the above-described object, the inventors of the present invention have found that the phosphorus concentration can be efficiently reduced even when the consumption amount of each material is suppressed in the steelmaking refining process of demolition, demolition and decarburization, and a heat source for scrap melting can be ensured, We also looked at ways to improve the withdrawal rate. As a result, in the charcoal preliminary treatment for performing the degassing treatment of the charcoal line and the charcoal dephosphorization treatment in the converter, at the time of decontamination treatment and / or the dephosphorization treatment and / By using a lance lance having a burner function with a combustion gas hole (burner hole) for supplying a fuel gas or a combustible gas at the same time in addition to the supply of the powder, The above objects can be realized more easily, and the present invention has been developed.

That is, the present invention relates to a method for converting steel into molten steel by decarburizing and de-phosphorizing the molten iron in the first converter and then decarburizing and refining it in the second converter, After the molten iron is charged, the molten iron is degassed by spraying the powder containing the refining oxygen and the lime-keeping solvent from the lance. Subsequently, a part of the slag is discharged after the degassing treatment, And then discharging the powder containing the refining oxygen and the lime-based insulating material from the lance to the bath surface of the molten iron after the degasification remaining in the furnace, And then,

Next, when the molten iron after the removal of the molten iron is discharged, at least a part of the slag is left in the converter after the removal of the molten iron, and then the molten iron after the removal of the molten iron is transferred to the second converter to obtain molten steel, It is possible to use either or both of the degreasing treatment and the dephosphorization treatment by using a lance having a burner function capable of spraying a refining oxygen, a powder containing a lime-keeping solvent, a fuel gas and a retarding gas It is a transformer steelmaking method which is characterized.

In the method of the present invention, it is preferable to employ the following means.

(1) The slag is left in the first converter after the dephosphorization treatment in an amount of 30 mass% or more generated in the previous (preliminary) dephosphorization process, and further, at least the untreated molten iron is charged into the first converter , Degreasing treatment of the charcoal is carried out by injecting a powder containing the refining oxygen and the lime-setting solvent, or further with a fuel gas and a retarding gas from a lance having a lancing function or a burner function, And then discharging at least 40 mass% of the exhaust gas to the outside of the furnace. Thereafter, in the first converter, powder containing the refining oxygen and the lime-setting solvent, And a deodorizing process of the molten iron by jetting a retarding gas

(2) a lance having the burner function at the time of decarburization refining,

(3) The burner combustion calorie supplied from the lance having the burner function which is used at the time of one or two or more of the dephosphorization treatment and the decarburization refining at the degumming treatment is 10 MJ / t or more,

(4) The lance having the burner function used for any one or two or more of the degasification treatment, the denitrification treatment, and the decarburization refining is a multi-pipe lance having a refining oxygen passage and a powder feed passage, a fuel gas passage, In fact,

(5) The powder may be obtained by introducing at least one of iron oxide material and manganese oxide together with a carrier gas composed of an inert gas such as argon or nitrogen,

(6) After slag removal, the slag shall retain at least 60 mass% of the amount generated during the slag removal process in the converter.

(1) According to the conversion steelmaking method of the present invention having the above-described structure, the limestone in the slag after the denitrification treatment can be utilized as a seam member in the following degasification treatment, and also in this case, It is possible to reduce the amount of lime-based polishing material used in the steelmaking process, particularly in the entire molten iron pre-treatment process.

(2) According to the present invention, in the molten iron preliminary treatment step, since the molten iron is intermediately discharged after the denitrification treatment and then the denitration treatment is carried out in the same converter, the heat dissipation- It can be used as a heat source, and the slag can be utilized as a solvent after high-temperature denitrification produced in the pre-charge. Therefore, as compared with the case where the solvent at room temperature is added, it is possible to utilize the endothermic component as heat for dissolving the cold iron source, further increase the amount of scrap iron used, can do.

(3) According to the present invention, in the molten iron pre-treatment step, since the slag of the low-salt air generated in the degreasing treatment is discharged to the outside of the furnace during the degreasing treatment and the denitration treatment, / Mass% SiO ₂ ) = 1.2 to 3.0) can be maintained. Therefore, the amount of the lime-based polishing solvent used in the denitrification treatment can be reduced.

(4) According to the present invention, by using a top-blowing oxygen transmittalance (hereinafter simply referred to as " burner function lance ") having a burner function capable of blowing powder, It is easy to discharge the slag of the low-salt air-stream to the outside of 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 lance having the burner function becomes the heat transfer medium, and the heat supply to the molten iron and slag can be performed with high efficiency. Therefore, It is possible to compensate for the thermal loss due to the addition of the iron oxide source and to reduce the loss of iron particles in the slag.

(6) According to the present invention, when the powder supplied from the burner hole of the lance having the burner function serves as the heat transfer medium, the powder is heated, so that the removal efficiency of the molten iron is improved by the flux, Contributes to the reduction promotion of Mn ore during decarburization refining, and it is possible to reduce the refining cost.

Fig. 1 is a schematic view of a converter-type vessel used in the pretreatment method.
2 is a process diagram of a preliminary hot water treatment method according to the present invention.
3 is a cross-sectional view of a lance having a burner function.
4 is a diagram showing the relationship between the amount of heat supplied from a lance having a burner function and the de-Si slag dis- placement rate.
5 is a graph showing the relationship between the amount of heat supplied from a lance having a burner function and [P] after de-P blowing.
6 is a graph showing the relationship between the amount of heat supplied from the lance having the burner function and the yield of Mn ore.

(Mode for carrying out the invention)

In a suitable transfer steelmaking method according to the present invention, preliminary treatment of a charcoal is performed using a converter, and decarburization refining is performed. As the converter, a vertically rotatable converter (refining furnace) 1 as shown in Fig. 1 is used. In the present invention, the molten iron in the converter 1 is subjected to the degassing treatment and / or the denitrification treatment in the lance 2 having the above-described ascendible burner function, that is, And is characterized in that oxygen gas for refining is injected (drawn out) from the front end of the charging / discharging lance 2 having a combustion burner function capable of blowing toward the bath surface (charcoal). As the oxygen gas, it is preferable to use pure oxygen for industrial use. Further, the take-out is carried out using the take-off air outlet 3 formed on the bottom of the converter 1. As the deodorizing gas, a gas containing oxygen gas or an inert gas such as an Ar gas or a nitrogen gas is generally used. However, a gas having a function of enhancing stirring of the molten iron to promote dissolution of the iron source by blowing into the molten iron, Gas or the like having the function of blowing the solvent into the molten metal together with the gas for the gas. Reference numeral 4 in the drawing denotes a hole for tapping the molten metal 9 after refining.

In the practice of the method of the present invention, for example, at least two converters are used, at least one of the converters (1) is used for the preliminary treatment of molten iron, and at least one of them is decarburized It is used for refining to produce molten steel. That is, in the present invention, it is preferable that pretreatment is carried out in the first converter for charcoal pretreatment, and charcoal after the pretreatment is transferred to the second charcoal for decarburization refining to perform decarburization refining.

The lance 2 having the burner function characteristic of the present invention is as shown in the sectional structure of Fig. As described above, this is an inexpensive burning lance having a burner function capable of blowing powder. The lance 2 having the burner function has a concentric 6 pipe structure and an inert gas such as Ar or N ₂ is used as a carrier gas to supply a burnt lime or an iron oxide powder, A powder blowing passage 18 for blowing one or more powdery refining materials (powders) out of other materials, and has a plurality of annular passages on the outside thereof. The annular passage has, in order from the inner side (inner pipe), a fuel gas passage 19, a further delayed gas passage 20 such as oxygen or air for combustion on the outer side thereof, And the cooling water passages 22a and 22b having a structure for reversing the inner and outer passages at the lower end are disposed in the passage 21 and the outermost portion of the outer side thereof. A lance tip 23 made of copper is attached to the lower end of the main body of the lance 2 by welding or the like.

In the present invention, the lance (2) having a burner function capable of supplying the refining powder as described above in place of the conventional lance feeding lance is adopted because the burner combustion heat is efficiently transferred to the molten metal Therefore, it is possible to effectively supply the amount of heat required for scrap melting and the like. In addition, since the refining powder injected from the lance becomes the heat transfer medium of the burner combustion heat and the refining powder itself is also added in the heated state, the slag temperature is raised to accelerate the disposal after the degreasing process, Thereby reducing the amount of lime used as the anticaking agent and improving the iron yield. In addition, when the lance 2 having the burner function is used in the charcoal clearance blowing, dissolution of the quartz member is promoted, so that the de-phosphorus reaction is improved. Further, in decarburization blowing, the use of the lance 2 also contributes to improvement of the reaction efficiency such as reduction promotion of Mn ore.

Hereinafter, as a part of the converter steelmaking method according to the present invention, a method of performing the preliminary treatment of the molten iron using the first converter 1 will be described with reference to Fig. As shown in the figure, the iron wire pretreatment method comprises the steps of (A) charging iron, (B) degassing treatment, (C) intermediate disposal, (D) Particularly, by repeating these steps in the same converter, efficient preliminary processing of the molten iron becomes possible. Hereinafter, examples in which a lance having the burner function is used in both of the degassing process and the denitration process will be described. Of course, the lance having the burner function may be used for only one of the processes.

(1) Charging line charging process (A)

In this step (A), at least a part of the slag (hereinafter, simply referred to as "demagnification slag") 17 generated in the preliminary treatment of the previous molten iron is subjected to heat treatment in the converter (refinery) A new hot wire 9 is charged from a charging ladle 14 or a cold iron source 11 such as an iron scrap is charged before the hot wire is charged and then the molten iron 9 is charged do. As the cold hearth 11 to be charged in advance in the converter type refining furnace 1, it is possible to use, in addition to the iron scrap specified in the "Uniform Standard for Scrap Steel Inspection" of the Japan Iron and Steel Association, iron as a main component .

In the converter 1, the de-phosphorus slag 17 generated at the time of the previous refining (the last charge) to be remained so as to prepare for the next refining (the next charge) regulates the slag basicity at the time of degasification treatment of the next charge There is a role. That is, the basicity (mass% CaO / mass% SiO ₂ ) (hereinafter simply referred to as "basicity") of the de-phosphorized slag is 1.2 or more, and preferably 1.4 or more. This is because, if the basicity of the deoxidized slag 17 of the former charge former is less than 1.2, it is insufficient to control the basicity in the denitrification treatment even if the deoxidized slag is remained, and it is necessary to add a large amount of the ladder- . The upper limit of the basicity is not particularly limited, but the basicity of the slag is not more than about 3.0 in the conventional iron wire-untreating treatment, so that there is no particular need to increase the basicity.

Further, in order to effectively control the basicity, the amount of the previously-charged dephosphorized slag 17 remaining in the furnace is preferably at least 30% by mass, preferably at least 60% by mass to 100% by mass %. In addition, if the total amount of the dead-charged slag 17 of the last charge remaining in the furnace is utilized for the degassing treatment of the next charge, the basicity in the degassing treatment can be more easily controlled. Further, when this method is continuously carried out, the pre-treated slag to be discharged becomes only the pre-processed slag at the time of the intermediate disposal, and the de-phosphorous slag having a high basicity is not discharged. Therefore, the expansion of the slag by the hydration reaction, There is no such problem. Therefore, the method of the present invention is also very effective in using the slag.

Further, the de-phosphorized slag 17 is relatively highly salt-resistant and has low fluidity due to its high solid phase ratio at a low temperature (about 1350 ° C or less). Therefore, an inefficient operation of adding a large amount of coolant to solidify the slag as in the case of leaving the decarburized slag in the furnace is not necessary from the hot water phase and the material dendritic phase. Further, the de-phosphorized slag 17 contains a large amount of fine metal iron in the structure because of its abundant solid phase and low fluidity from the above characteristics, and even after the slag is subjected to charring treatment after pulverization, It contains iron. Conventionally, this is discharged to the outside of the system as slag. However, according to the present invention, since this is delayed by the next charge together with the slag, most of the metal iron in the slag is recovered into the molten iron to reduce the loss of the iron source.

Further, with respect to the slag at the end of the degassing process (hereinafter, referred to as "pre-degassed slag"), since the liquid phase rate is high and the fluidity is relatively high, the metal iron in the slag is easily separated, So that the amount of metal iron remaining in the slag is small. Therefore, in the method of the present invention, the iron loss into the slag can be reduced through the whole iron pre-treatment.

(2) Denitration process (B)

In this step (B), the converter 1 is uprighted, the refining oxygen gas 5 is injected mainly from the lance 2 or the like having the burner function toward the molten iron line 9, And the degassing is performed by simultaneously injecting the combustion oxygen, the fuel gas 7, and the refining powder, which are the retarding gas 6, at the same time. Particularly, this decalcification process is characterized in that a refining powder composed of a silicon source 15 and a lime-keeping solvent 16 accommodated in a hopper 8 is supplied to the central passage 18 of the lance 2 having the burner function, In a combustion atmosphere by a burner. If necessary, these powders may be supplied from chutes (not shown). At this time, the lance 2 having the burner function is heated by the burner function of the delayed gas 6 and the fuel gas 7, so that the carbonaceous material, the silicon source, or the oxygen source, which serves as the heat source, And the like may be added in the same manner. From the viewpoint of dissolving a large amount of the cold hearth 11, the oxygen source for the degassing treatment is preferably an oxygen source for removing oxygen from the refining oxygen gas passage 21 of the lance 2 having the burner function, It is preferable to inject only the liquid (5).

The silicon contained in the molten iron 9 or the silicon source 15 contained in the molten iron 9 and the silicon contained in the molten iron 11 and converted into molten iron by melting are reacted with an oxygen source (Si + O ₂ ? SiO ₂ ), So that the reaction efficiency in the subsequent denitrification treatment can be increased. During this degumming treatment, oxidation heat is generated. As a result of this oxidation heat, the molten iron temperature rises and the dissolution of the cold iron source 11 in the molten iron is accelerated.

The composition of the slag in this degasification step is determined in consideration of the amount of the previously removed charge of slag 17 previously retained in the furnace and the estimated value of the composition thereof and the amount of silicon dioxide produced by the reaction, Of the slag is adjusted to be 0.5 or more and 1.5 or less. When the basicity is less than 0.5, the concentration of phosphorus in the molten iron is increased due to the deoxidizing slag 17 of the last charge remaining in the furnace, and the denitrification load in the subsequent step becomes large, which is not efficient. Therefore, the basicity of the degassed slag at the end of the degassing treatment is set to be 0.5 or more, more preferably 0.7 or more. When the basicity is higher than 1.5, the fluidity of the slag is lowered, so that there is a problem that the amount of disposal at the time of the subsequent intermediate disposal becomes smaller and the control of the disposal amount becomes difficult, which is also effective in reducing the lime- not. Therefore, the slag basicity at the end of the degassing treatment is set to 1.5 or less, more preferably 1.2 or less. Further, for controlling the basicity, steel slag selected from decarburized slag, deinked slag, ladle slag, etc. is used as a slab material in addition to a lime slurry such as burnt lime, limestone and dolomite.

The molten iron temperature at the end of the degassing treatment is controlled to be 1260 DEG C or higher and 1450 DEG C or lower, more preferably 1400 DEG C or lower. When the temperature is higher than 1450 DEG C, the deinking slag 17 remaining in the furnace causes an increase in the concentration of the molten iron in the furnace. Therefore, the unloading load in the subsequent process becomes large and not efficient, It is also necessary to raise the magnesia concentration in the slag in order to prevent damage to the carbon brick, which is costly. On the other hand, when the temperature is less than 1260 占 폚, the flowability of the slag is lowered, the amount of discharged material at the time of the next intermediate discharge is decreased, and the control of the discharge amount becomes difficult.

In addition, the control of the molten iron temperature at this stage is also effective for efficient removal of the molten iron in the subsequent degumming step. For example, when the molten iron temperature at the end of the degassing treatment is 1350 占 폚 or less, the amount of the coolant to be added, such as iron ore, to be added for temperature control in the denitration treatment can be greatly reduced. In the present invention, since the degasification treatment and the degumming treatment are continuously carried out in the same converter, there is also a problem that it is difficult to charge the scrap before the removal treatment in terms of the working time. In addition, since the cold weather iron such as scrap that can be input from the furnace during the processing is limited in quantity, such as a set price, or in a steel mill now, it is difficult to normally use it in large quantities. Actually, there is a possibility that the cold iron source can not be input from the furnace because of the limitation of the number of kinds of the sub materials which can be used in the furnace injection device. In short, conventionally, the coolant used in the dephosphorization process is limited to iron oxide such as iron ore, and a cold iron source such as cheap scrap is not fully utilized.

In the degreasing step, it is relatively easy to increase the amount of cheap scrap used, so that the molten iron temperature after the degreasing treatment can be lowered to 1400 占 폚 or lower. However, the dissolution rate of the scrap is largely influenced by the molten iron temperature, and substantially the heat supply is required. Further, when the Si concentration of the molten iron is high, the adjustment of the basicity during the demineralization may not be sufficient with only the limestone in the demineralized slag 17 remaining in the furnace. In this case, in the present invention, a new stone member such as decarburized slag may be added using the burner-containing lance 2 or a chute. It is effective for promoting the dissolution of the added stonewall member in the slag-removing property after the degumming treatment and the reduction of the stitching loss in the waste slag, and the use of the burning lance 2 with the burner function is surely advantageous. We exert power for improvement of point.

When the content of the molten iron is low, the scrap may melt and the remainder may be generated. However, the molten iron may be retained (held) with the molten iron as it is in the converter, and then melted to the next dephosphorization step. That is, with respect to the cold iron source, if the dissolution is completed until the end of the denitration process, the problem of operation does not occur.

Further, the molten iron temperature after the degassing treatment may be a measured value by a thermocouple or the like, or a calculated value from heat storage may be used. For example, the calculation method from the heat storage can be calculated based on the following expression (1), but it is not necessarily limited to this. It tends to be slightly higher than the calculated value by adding or subtracting a variable, depending on the individual apparatus condition or operating condition, but it is an error degree.

T: molten iron temperature after degassing treatment (캜)

T _i : Charging temperature (° C)

X _p : The basic unit of the charter (kg / t)

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

X _Si : Basic unit of silicon to be oxide (kg / t)

X _C : Carbon intensity in additives (kg / t)

X _ore : Iron oxide unit weight (kg / t)

X _O2 : Gaseous oxygen content (Nm 3 / t)

X _f : Each piece of steel (kg / t)

W: Transferring molten iron capacity (t)

X _t : Time (min) from the charge exit to the end of degrade processing

The silicon (X _si ) to be an oxide in the above-mentioned formula (1) is the sum of those contained in molten iron, cold iron sources, additives and the like. Among them, the silicon concentration in the charcoal uses the quick analysis value of the sample collected from the charcoal before charge charging. However, it is also possible to use a substitute method such as calculation by using other analytical values such as an exit component of the blast furnace. The silicon concentration in various cold hearth sources is, for example, an analytical value of a representative sample for each lot, but it is often stable in a concentration of about the same as that of molten iron in cold waters. The silicon concentration in the scrap is stable at a concentration of 1/10 or less of the average value of the pig iron, although there is fluctuation caused by the generation source. Therefore, this value may be used as a representative value or ignored.

Among these additives, silicon is not an oxide. As a typical additive, a powder containing about 60% by mass of silicon carbide is formed into briquettes in addition to ferrosilicon, though it is contained as silicide iron, metal silicon, silicon carbide, silicon nitride or other silicide. (Hereinafter referred to as silicon carbide briquettes), and the like.

As an analysis method of silicon which is not an oxide in the additive, in addition to the method of analyzing ferrosilicon described in JIS G 1312, there can be used a method of analyzing silicon in addition to the method of total silicon analysis, acid-soluble silicon analysis, Thermal mass analysis, carbon analysis by a combustion method adjusted for temperature history, analysis of other contained elements, and analysis of compounds by X-ray diffraction.

Among the additives, there is carbon. As the carbon source, in addition to the carbonaceous materials such as coke or amorphous graphite, carbon is used among carbides such as silicon carbide described above. In addition, additives such as burnt lime, light-burned dolomite, and magnesia clinker are used as additives. In addition, slag such as demineralized slag, decarburized slag, and ladle slag is also used as a calcium oxide source or a magnesium oxide It can be used as a circle. As an inexpensive additive, carbonates or hydroxides of calcium or magnesium may be used. However, when they are used in a large amount, it is preferable to modify formula (1) described above, Do.

As described above, in the degasification treatment of the present invention, since the molten iron temperature after the treatment is controlled to an appropriate range and silicon is used as the heat source, a large amount of cold iron such as 100 to 300 kg / It is possible to efficiently dissolve the cold iron source and perform the preliminary treatment refining of the molten iron without lowering the productivity or raising the refining cost even if the round is used. However, when the cold rolling source unit load is 300 kg / t or more, a further heat source is required, which leads to an increase in cost, and a long time for the winding, resulting in a decrease in productivity. Further, it is not efficient to further increase the amount of use even from the restriction of the charging facility of the cold hearth source.

Although it is described later, it is preferable to cause appropriate foaming of the slag in the molten steel pre-treatment converter 1 in order to increase the slag, that is, the removability of the pre-formed slag 10 after degumming treatment. For this purpose, it is effective to increase the generation rate of CO gas generated by the reaction of carbon in the molten iron and iron oxide in the slag. Therefore, in order to obtain a stable slag removing ratio in the subsequent disposal step, it is preferable to supply oxygen over the stoichiometric amount necessary for oxidizing silicon in the charcoal and the added silicon source.

It is preferable that the initial amount of oxygen supplied to the molten iron during the degassing treatment is 2 Nm 3 / t or more, preferably 4 Nm 3 / t or more, in addition to the amount required for degassing stoichiometrically. In the present invention, the silicon concentration in the molten metal at the time of completion of the degassing treatment is set to 0.1 mass% or less, preferably 0.05 mass% or less, by carrying out such oxygen transmittal. This makes it possible to keep the foaming state even when discharged after the degreasing treatment, to keep the excretaability favorable, and to suppress the blooming from the slag to the molten iron. In the study by the inventors, it was found that the rate of air transfer from the lance 2 having the burner function is 1 to 3 Nm 3 / min · t and the blowing rate of the take-off gas is in the range of 0.1 to 0.6 Nm 3 / min · t, Effect is obtained. As for the determination of termination of the degasification treatment, in order to carry out the slag discharge by progressing the decarburization reaction as described above, the exhaust gas concentration during desulfurization, the CO, the CO ₂ concentration in the exhaust gas, the exhaust gas flow rate, It is appropriate to determine while monitoring the decarburization rate calculated from the gas analysis value.

(3) Intermediate disposal step (C)

In the present invention, in the preliminary treatment of molten iron, a step of discharging the demineralized slag is formed after the above-mentioned degreasing treatment. In the disposal step (C), the degassed slag of the low-salt air-phase containing a large amount of SiO ₂ generated during the degassing treatment is discharged from the converter 1. The discharge of the so-called degassed slag 10 is effective for obtaining an appropriate slag basicity in the denitration treatment in the next step and for reducing the amount of the lime-based polishing material used. Further, in the case of the pretreatment method of molten iron for performing the demolding treatment of new molten iron in the next charge while remaining the remaining molten slag 17 in the furnace in a large amount in the furnace, the molten iron is degasified to prevent the molten slag 17 from leaking from the slag to the molten iron. The concentration of phosphoric acid in the desulfurized slag becomes higher than the conventional one. Therefore, if the degassed slag is remained in a large amount in the converter 1, the amount of phosphoric acid in the furnace slag in the subsequent denitrification process becomes excessive and the denitrification effect is lowered. In order to prevent this, (C) is important. In addition, the intermediate waste after the completion of the removal of the cannulation may be discharged from the furnace outlet by tilting the converter, or from the hot-water hole 4 of the charcoal.

In the method for pretreating molten iron by the first converter (1) in the conversion steelmaking method according to the present invention, since the processes of these steps (A) to (C) are repeatedly and continuously carried out, Care must be taken in the accumulation of phosphoric acid into the furnace. If the amount of phosphoric acid in the slag is excessively large in the step of removing the phosphorus in the step of removing phosphorus, the efficiency of the phosphorus removal reaction is lowered due to the increase of the phosphoric acid concentration in the slag, thereby increasing the phosphorus concentration in the phosphorus after the treatment, There is a problem in that the amount of use of the resin is increased.

To solve this problem, in the present invention, the lance 2 having the burner function is used. One example of suitable conditions for the degassing treatment of the present invention is shown in Table 1 and the effect is shown in Fig. As can be seen from Table 1 and FIG. 4, by using the lance 2 having a burner function, it becomes possible to effectively supply heat to charcoal and slag, and it is possible to dissolve scrap, lime, promote the melting of the iron oxide source, It is possible to stabilize the intermediate dis- charge rate by the above-mentioned method, and to reduce the torsion in the intermediate disposal slag.

That is, in the same denitrification condition, instead of the method of charging the scouring agent according to the conventional method, when the powder as the scouring scouring agent is added using the lance 2 having the burner function as in the present invention, The blowing powder such as the refining flux is heated before reaching the bath surface, so that the melting of the slag is more efficient. That is, as shown in Fig. 4, when attention is paid to the intermediate disposal, when the heat supply of 10 MJ / t or more is performed in the lance 2 having the burner function, the rejected slag disposal rate is remarkably improved. As a result of observing the molten irregularities suspended in the slag, it was found that the lance 2 having a burner function having a burning temperature of 10 MJ / t or more was 10 mass% in the case of a typical lance having no burner, And when it was used, it was reduced to 6 mass%.

(Table 1)

In addition, if most of the generated degassed slag is discharged, the commodity of the lime-based lime additive newly added in the next step of the denitrification treatment is delayed, which is an impediment to the denitrification. With respect to this problem, fluorite can be added to accelerate the commodity. However, as described above, the application of the generated slag is restricted, making it difficult to treat the slag. In addition, there is a method of promoting the commodity by adding iron oxide such as iron ore. However, this method is not advantageous because the heat loss due to the decomposition endothermic reaction of iron oxide is large and the amount of heat available for dissolving the cold iron source decreases.

Therefore, regarding the reject rate in the intermediate disposal process, the following countermeasure is taken. That is, it is preferable that the excretion rate (mass%) of the demineralized slag = (exhaust slag mass) × 100 / (total internal slag mass at the end of the regeneration treatment)) is at least 40%, preferably 60% . This is because, if the exclusion ratio is less than 40 mass%, the amount of the lime-based polishing solvent used in the next step of the denitrification treatment is increased as described above. In addition, if the amount of residual slag is increased, slag forming can not be suppressed, and slag ejection from the furnace slag occurs at the time of the denitration process, which may result in malfunction due to the slag ejection.

In the present invention, the basicity of the slag at the end of the degassing treatment is controlled to fall within the range of 0.5 to 1.5, and the molten iron temperature at the completion of the degassing treatment step is controlled to 1260 DEG C or more and 1350 DEG C or less, do. This makes it possible to ensure good fluidity of the slag and gas hold-up, so that good scraping can be carried out only by tilting the rotor after the completion of the degasification treatment and discharging the slag from the furnace. With respect to this point, when the slag is flowed out by adjusting the tilting angle of the furnace so as not to discharge the molten iron, a certain amount of slag can not be left in the furnace, but the forming slag has a higher specific gravity than the true specific gravity Since the volume specific gravity is reduced, the amount of slag remaining in the furnace can be controlled to be low.

(4) Dephosphorization process (D)

After the disposal step (C), the powder containing the lime-scavenging agent, a scouring scouring agent, and an oxygen source are supplied to the charcoal remaining in the same one converter (1), and the charcoal is subjected to a deodorization treatment. It is preferable to use only the oxygen gas (5) from the lance lance (2) having the above burner function in order to reduce the thermal loss. The phosphorus in the molten iron is oxidized by oxygen in the supplied oxygen source to become phosphorus oxide (P ₂ O ₅ ), and the phosphorus is stably introduced into the slag produced by the commodity of the lime-setting anticorrosive agent, . In order to efficiently carry out the denitration reaction, the lint (2) having the burner function or the chute is used to adjust the basicity of the slag after the denitrification (the charge-taking descainant slag (17) It is preferable to carry out the dephosphorization treatment so that the temperature of the molten iron after the completion of the dephosphorization treatment is 1280 DEG C or higher and 1360 DEG C or lower.

(Table 2)

The reason for this is that when the slag basicity of the drawn-up slag 17 of the current charge generated during the demethanization treatment is less than 1.2 or the molten iron temperature is more than 1360 ° C, the demineralization capacity of the slag is lowered, There is a case in which it can not be lowered. On the other hand, if the basicity of the slag is more than 3.0, the cost of the lime-setting agent becomes difficult, the cost of the lime-setting agent increases, and even if the lime temperature is less than 1280 캜, The amount of heat at refining is insufficient. In order to secure a sufficient amount of heat at the time of decarburization refining by other electric converters performed thereafter, the temperature of the molten iron after the completion of the denitration treatment is set to 1280 ° C or higher and 1360 ° C or lower, % Or more, and the amount of oxygen used and / or the amount of carbon added in the denitrifying treatment and the denitrifying treatment are adjusted.

The effect of applying the lance 2 having the burner function in the de-phosphorization step (D) is as shown in Fig. That is, in the lance 2 having the burner function, the de-phosphor powder such as lime or iron oxide becomes the heat transfer medium of the burner combustion heat, the deinking agent itself is heated and the mass transfer of the deink agent component is promoted, . This is because, as shown in FIG. 5, when heat of 10 MJ / t is supplied as heat of burner burning through the lance 2 having the burner function, the amount of [P] Can be understood.

(5) tapping process (E)

In this step (E), when the concentration of phosphorus in the molten iron has decreased to a predetermined value through the above-mentioned dephosphorization step (D), the converter (1) is tilted to the side where the tapping tunnel is installed, (Not shown).

(6) Decontamination refining

After the molten iron preliminary treatment with the first converter (1) comprising the above steps (A) to (E), the demineralized charcoal boiled out is next subjected to decarburization refining, that is, a second converter And decarbonized to refine a predetermined molten steel. In this step, since the decarburization treatment is carried out using the deoxidized molten iron, it is not necessary to lower the end carbon concentration and to improve the denitration by promoting the formation of FeO in the end point slag. Therefore, for example, Do. However, for reduction of Mn ore, it is necessary to compensate the reduction heat and improve the Mn ore reduction efficiency. In this regard, if the lance 2 having the burner function is used under the conditions shown in Table 3, it is effective as shown in Fig. That is, as shown in Fig. 6, in the case of performing the Mn ore reduction in the decarburization refinement converter, the lance 2 or the chute having the burner function mainly of Mn ore is used and the heat supply amount from the burner is 10 MJ / , It is possible to compensate the heat during reduction of the Mn ore, and at the same time, the reduction efficiency is improved, contributing to the improvement of the Mn yield.

(Table 3)

As described above, in accordance with the present invention, in the converter steelmaking method for preliminary treatment and decarburization refinement of molten iron using a converter, after the molten iron has been subjected to the removal of the molten iron after the boiling, at least a part of the slag is removed So that a new charcoal is charged and a degasification process is performed. Therefore, most of the slag discharged from the converter type refining furnace (pretreatment furnace) becomes a desulfurization slag. As described above, the degassed slag has a relatively low basicity and little incorporation at present, so that there is no problem of expansion due to alkali leaching or hydration reaction. Particularly, in the method of not discharging the descaling slag at all, such a problem does not occur at all, so that the processing of the slag can be simplified, and the present invention can be applied to high value-added uses. In order to achieve efficiency and stabilization of a process having such characteristics, the present invention uses a lance lance having a burner function, and it is possible to improve the reject rate after degasification and reduce the tritium in the slag.

Example 1

First, the charcoal pretreatment was carried out using the converter 1 having a capacity of 300 tons as shown in Fig. In this process, oxygen gas for refining is sprayed toward the bath surface (molten iron) using the lance 2 having the burner function shown in Fig. 3, and the molten iron Nitrogen gas was blown therein. However, when the burner lance is not used, a fuel gas passage 19 and a quadruple lance without delay gas passage are used in Fig. The conditions of the decarburization refining in the conversion furnace for the pre-treatment of the molten iron in the pre-treatment converter are shown in Tables 1 to 3, but the iron component and the like are shown in Tables 4-1 to 4- Respectively. The results of the dewaxing are shown in Table 4-1, the results of the dewatering are shown in Table 4-2, and the results of the dewatering are shown in Tables 4 and 3, respectively. In these embodiments, as the previous step, a part of or all of the slag after the dephosphorization treatment generated in the hot-wire dephosphorization treatment is left in the furnace, the hot iron source is first charged into the furnace, Then, the oxygen for refining is turned over from the lance 2 having the burner function to start the degassing. Subsequently, after the degassing is performed, the degassing is carried out in the same converter, and thereafter, Is an example. The basicity of the slag generated in the denitrification treatment can be adjusted by adding lumpy lime to the shot or pulverized lime from the powder blowing passage 18 of the lance 2 having the burner function did. In addition, the termination of the denitrification (treatment) in the preliminary treatment of the molten iron was judged by the change of the exhaust gas temperature and the CO concentration in the exhaust gas. The intermediate reject rate in the table was evaluated by weighing the slag lays.

As is clear from Tables 4-1 to 4-3 shown as Comparative Example 1 and Inventive Examples 1 to 9, both of the treatments at the time of detaching and demagnetizing are not using a lance having a burner function (Comparative Example 1 ), The intermediate reject rate is poor, and the P concentration after the P removal is high. Further, in the examples (Inventive Examples 1 to 3) in which a lance having a burner function is used at the time of detachment blowing and a lance having the burner function is not used at the time of demineralisation, the P concentration after detaching is slightly higher, The intermediate reject rate was improved for Comparative Example 1 in which no lance having a burner function was present at the time of blowing. Further, in the case of using the lance having the burner function (Inventive Examples 2 and 3), the intermediate reject rate was further improved at the time of removing the exhaust gas, although a sufficient amount of heat was added from the lance having the burner function at the time of detachment blowing. In this respect, at least in the stage of cannistering, it has been found preferable to use a lance having a burner function.

In addition, when a lance having the above-described burner function is used at the time of detoning and demagnetization and the amount of heat applied is adjusted to 10 MJ / t or more, both the intermediate reject rate and the phosphorus concentration can obtain preferable results (Examples 4 to 9 ). It was also found that when the lance having the burner function was used for decarburization under the same conditions, the Mn yield was improved (Examples 8 and 9). In particular, it has been found that favorable results can be obtained at any point of the intermediate reject rate, the CaO basic unit, and the Mn yield by using the lance having the burner function in each step of degreasing, demagnetization and decarburization.

(Table 4-1)

(Table 4-2)

(Table 4-3)

Example 2

This example shows the result of examining the influence of the removal rate of the de-phosphorized slag at the time of demagnetization. In this embodiment, the electric conduction, the burner, etc. used were the same as those in Example 1, and the conditions for blowing were also basically performed under the same conditions as in Example 1. However, the operation for changing only the removal rate of the removed slag Condition. The results are shown in Tables 5-1 to 5-3.

As is clear from the results shown in Table 5-1, according to Inventive Examples 10 to 15, as compared with Comparative Example 2, in the detonation blowing at the next charge after leaving a part (50 to 100%) of the exfoliated slag, It was found that the improvement of the intermediate dislocation rate and the decrease of the CaO addition amount were achieved. As is apparent from the results shown in Table 5-2, it was also found that there was no significant difference between Examples 10-15 and Comparative Example 2. In addition, as shown in Table 5-3, it was found that the total Fe yield and the total CaO basicity were improved in a series of treatments such as desiliconization, degumming, and decarburization refinement.

(Table 5-1)

(Table 5-2)

(Table 5-3)

The present invention is related to a steelmaking method of a converter, but it is obviously also effective as a so-called pretreatment technique of molten iron.

1: Converter
2: Upper lance with burner function
3: Outlet tuyere
4: Tapping area
5: Oxygen gas for refining
6: Delayed gas
7: Fuel gas
8: Hopper
9: Charter
10: Degassed slag
11: Cold iron circle
14: loading ladle
17: Thinner slag
18: Powder intake path
19: fuel gas passage
20: retarding gas passage
21: Oxygen gas passage for refining
22a: cooling water passage
22b: cooling water passage

Claims (7)

In a first converter, decalcification treatment and de-phosphorus treatment are performed together with decarburization treatment of a molten iron, and then decarburization refining is conducted in a second converter to make molten steel,
First, after charging a charcoal in the first electric furnace, the charcoal is degassed by spraying a powder containing refining oxygen and a lime-based insulating material from the lance,
Subsequently, the slag is removed from the slag after the degassing treatment, and the remaining slag is left in the vessel along with the molten iron.
Next, the deodorizing process of the charcoal is carried out by spraying the powder containing the refining oxygen and the lime-based insulating material from the lance on the bath surface of the charcoal which has been left in the electric furnace,
Next, the molten iron after the removal of the molten iron is discharged, and at least a part of the slag is left in the converter after the removal treatment,
Thereafter, when molten iron after the boil-off deinking treatment is transferred to the second converter to obtain molten steel by decarburization refining,
Wherein the treatment of either or both of the degreasing treatment and the dephosphorization treatment is carried out by using a lance having a burner function capable of spraying a refining oxygen, a powder including a lime-keeping solvent, a fuel gas and a retarding (flammable) Is carried out by using an electric wire. The method according to claim 1,
The slag is left in the first electric furnace after the removal of the amount of 30 mass% or more of the amount generated in the previous (preliminary) dephosphorization process, and further, at least the untreated molten iron is charged into the first electric furnace, Or a powder containing a refining oxygen and a lime-equivalent material from a lance having a burner function, or further spraying a fuel gas and a retarding gas,
Subsequently, the intermediate slurry was discharged so that at least 40% by mass of the slag after degumming treatment was discharged to the outside of the furnace,
Thereafter, a powder containing the refining oxygen and the lime-setting material, or further a fuel gas and a retarding gas are sprayed in the first electric furnace by using a lance having a function as a lancing lance or a burner, (1). 3. The method according to claim 1 or 2,
Wherein the lance having the burner function is used at the time of decarburization refining. 4. The method according to any one of claims 1 to 3,
Wherein the calorific value of burner burning supplied from the lance having the burner function at the time of one or two or more of the demineralization treatment and the decarburization refining at the demineralization treatment is 10 MJ / t or more. 5. The method according to any one of claims 1 to 4,
The lance having the burner function used in any one or two or more processes of the degreasing process, the denitrification process, and the decarburization refining is characterized by being a multi-pipe lance having a refining oxygen passage and a powder feed passage, a fuel gas passage, Steelmaking method. 6. The method according to any one of claims 1 to 5,
Wherein the powder is blown with at least one of an iron oxide material and a manganese oxide together with a carrier gas composed of an inert gas such as argon or nitrogen in addition to each of the solvent and the subsidiary raw material. 7. The method according to any one of claims 1 to 6,
Wherein the slag after the denitrification treatment leaves at least 60% by mass of the amount produced during the denitration treatment in the converter.

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