WO2003029498A1

WO2003029498A1 - Method for pretreatment of molten iron and method for refining

Info

Publication number: WO2003029498A1
Application number: PCT/JP2002/010108
Authority: WO
Inventors: Hiroshi Hirata; Hiromi Ishii; Hiroaki Hayashi; Yuji Ogawa; Naoto Sasaki
Original assignee: Nippon Steel Corporation
Priority date: 2001-09-27
Filing date: 2002-09-27
Publication date: 2003-04-10
Also published as: EP1457574A4; JP2003105418A; EP1457574A1; KR100658807B1; KR20040033326A; EP1457574B1; JP3854482B2

Abstract

A method for the pretreatment of a molten iron wherein use is made of a top-blown refining vessel, and the desiliconization and the dephosphorization of the molten iron are carried out by blowing a flux having a primary component which contains iron oxide and at least one of calcium oxide and limestone into the molten iron, characterized in that a carbon source is blown into the molten iron during desiliconization and the blowing of the carbon source is started prior to the start of the blowing of the flux. The blowing of the flux is preferably started after a [Si] concentration has been lowered to 0.15 mass % and/or after the blowing of the carbon source has been completed. The above method for the pretreatment of a molten iron and refining allows the refining which does not use fluorspar both in the pretreatment of a molten iron and the decarbinization steps, the minimization of formation of a slag for dephosphorization in the decarbonization step, and the improvement of the degree of allowance of heat through the efficient addition of a carbon source into a molten iron.

Description

Description Hot metal pretreatment method and refining method

The present invention relates to a hot metal pretreatment method for performing desiliconization and dephosphorization of hot metal using a refining vessel capable of being blown up and down, and a hot metal refining method for performing decarburization processing of hot metal after the hot metal pretreatment. Background art

Instead of the converter steelmaking method in which the hot metal is desiliconized, dephosphorized, and decarburized all at the same time in the same converter, prior to decarburization, the desiliconization and dephosphorization of the hot metal are carried out in a separate container from decarburization. Hot metal pretreatment methods have been used. In the pretreatment of hot metal, it is common to initially perform a desiliconization process by adding a solid oxygen source such as iron oxide to the hot metal and then dephosphorizing by adding a dephosphorizing flux to the hot metal. there were. In dephosphorization, a lime source was added as a flux to form a highly basic dephosphorized slag, and a solid oxygen source such as iron oxide was also added as a flux for dephosphorization. As a preliminarily dephosphorizing container, a torpedo car or a ladle was used, and a method of preliminarily dephosphorizing by injecting a dephosphorizing flux into the hot metal contained therein was used. Note that the solid oxygen, iron oxide and that of oxygen contained in the (FeO, Fe ₂ 0 ₃₎ in a solid oxygen source, iron ore, Dust which need use as a flux or coolant mill A material containing iron oxide such as a scale 5.

Recently, a converter-type refining vessel capable of top-bottom blowing has been used as a hot metal pretreatment vessel, and hot metal pretreatment for simultaneous desiliconization and dephosphorization of hot metal has been used. It has come to be. Since strong stirring by top and bottom blowing is used, dephosphorization can be promoted even with slag having a low basicity, so that desiliconization and dephosphorization can be performed simultaneously. Since gaseous oxygen can be sufficiently used as an oxygen source, the temperature of the hot metal after the pretreatment is higher than in the conventional case where only solid oxygen is used or gas oxygen is used in a very small amount. Can be maintained, and the processing time can be reduced compared to the pre-treatment using a torpedo car.Therefore, the temperature loss during the pre-treatment is small, and the overall heat tolerance including the decarburization treatment is ensured. be able to. The pretreatment refining flux may be added to the refining vessel from above by means of injection, or by injection by adding the bottom blown gas into the hot metal as a carrier gas. By employing the flux injection, the dephosphorization efficiency in the pretreatment can be improved.

In hot metal dephosphorization, the lower the hot metal temperature at the end of pretreatment, the higher the dephosphorization capacity. Therefore, even though the thermal margin can be improved by using gaseous oxygen in the pretreatment, if the hot metal temperature after the pretreatment is increased unnecessarily, the dephosphorization ability in the pretreatment is sufficiently exhibited. You cannot do that.

In hot metal desiliconization and dephosphorization, refining is performed by adding an oxygen source, so the carbon in the hot metal is inevitably oxidized and decarburization progresses, which is one of the causes of loss of heat tolerance during decarburization processing. It has become.

If a carbon source is added to the hot metal during the hot metal pretreatment or decarburization refining, it can be used as a heat source during the decarburization process, and the heat tolerance of the refining can be increased. As a method of adding a carbon source during the decarburization process, a method of adding lump anthracite from above is conceivable, but there is a problem that the outlet of the gas generated due to the upward flow of gas generated by blowing acid is large. . Moreover, because of the S i0 ₂ Inpu' bets from carbonaceous material, decarburization [0108] In order to secure the basicity of the slag at the time, it is necessary to increase the amount of quicklime, which is not preferable.

As a method for adding a carbon source during desiliconization and dephosphorization hot metal pretreatment, Japanese Patent Application Laid-Open No. Sho 62-170409 discloses a method for improving the slag slag property (Mn ore or Flux mixed with calcium fluoride (fluorite) etc. is added to the upper part, and desiliconized flux (iron oxide) is blown into the hot metal, and a gas Z solid oxygen source is supplied to the hot metal surface while the desiliconized flux is supplied. Alternatively, a method is described in which a carbon source is blown into the hot metal with a carrier gas after the completion of the desiliconization reaction to increase the carbon concentration of the hot metal. The reason for adding CaO-based flux to the upper part is that when CaO-based flux containing iron oxide used for dephosphorization is injected into the hot metal together with the carbon source, the oxygen potential in the hot metal due to the carbon injection is increased. The reason is that the dephosphorization reaction is inhibited and the phosphorus content is reduced.

In smelting, the use of fluorite increases the erosion of refractories in refining vessels used for pretreatment and decarburization. For example, as shown in FIG. 6 of JP-A-81-157921, it is known that the refractory erosion index increases as the fluorine concentration in the slag increases, and the refractory erosion increases rapidly. ing. Therefore, it is preferable not to use fluorite from the viewpoint of extending the life of refractories.

In the invention described in Japanese Patent Application Laid-Open No. Sho 62-170409, in which a carbon source is blown into the hot metal during the hot metal pretreatment, the flux is added upward, so that calcium fluoride (fluorite) or the like is used to ensure slag fluidity. It is necessary to add a slag-forming improver, and it is not preferable to go back to the direction in which fluorite is not used. Here, if fluorite is not used in the pretreatment, the dephosphorization ability in the pretreatment is insufficient, and it is necessary to form dephosphorized slag using fluorite in the next decarburization process and perform dephosphorization. Becomes

Pretreatment of hot metal in which desiliconization and dephosphorization are performed in the same container without waste In hot metal smelting, which is followed by decarburization, it is difficult to perform sufficient dephosphorization after pretreatment with conventional hot metal pretreatment, and slag must also be formed and dephosphorized in decarburization. was there. The formation of dephosphorized slag in the decarburization process causes an increase in cost.Furthermore, the use of fluorite to form the dephosphorized slag in the decarburization process negates the direction in which fluorite is not used. It will be.

The present invention enables refinement without using fluorite in the hot metal pretreatment and decarburization processes, minimizes the formation of dephosphorization slag in the decarburization process, and efficiently adds a carbon source to the hot metal. It is an object of the present invention to provide a hot metal pretreatment method and a refining method for improving the heat tolerance. Disclosure of the invention

With the conventional method, in which iron oxide is mainly blown into the hot metal together with a carrier gas as the oxygen source for desiliconization during the early stage of the hot metal pretreatment, the hot metal temperature cannot be sufficiently increased during the desiliconization reaction. However, the slag of the refining slag becomes insufficient. On the other hand, when gaseous oxygen is used as the oxygen source for desiliconization, the temperature of the hot metal rises remarkably during the desiliconization reaction, and the slag for dephosphorization and refining can be sufficiently slagmed. Can be performed efficiently.

When mainly blown gaseous oxygen is used as the oxygen source for desiliconization, the amount of flux blown into the hot metal during the desiliconization reaction can be significantly reduced. Therefore, if the carbon source as a heat source is blown into the hot metal together with the carrier gas at the time of the desiliconization reaction, it becomes possible to add only the carbon source into the hot metal before the start of the flux blowing. Since the dephosphorizing flux containing lime-based components and the carbon source are not injected at the same time, the dephosphorization is not hindered by the injected carbon. In addition, by eliminating simultaneous injection of carbon source and iron oxide-based flux, This also has the effect of eliminating the risk of ignition due to the reaction between the carbon source and iron oxide.

That is, by mainly using top-blown gaseous oxygen as the oxygen source for desiliconization and simultaneously injecting a carbon source as a heat source into the hot metal during the desiliconization reaction, the dephosphorization efficiency in the hot metal pretreatment is greatly improved and the refining is improved. It has been clarified that the overall thermal tolerance can be improved at the same time.

The present invention has been made based on the above findings, and the gist thereof is as follows.

(1) Using a refining vessel that can be blown from the top to the bottom, a flux containing one or more of quick lime, limestone, and iron oxide and containing at least iron oxide as a main component is blown into the hot metal to remove hot metal. A hot metal pretreatment method for performing silicon dephosphorization, wherein a carbon source is blown into the hot metal during the desiliconization reaction, and the carbon source blowing is started before the flux blowing is started.

(2) The hot metal pretreatment method according to the above (1), wherein the blowing of the flux is started after the [Si] concentration has decreased to 0.15% by mass.

(3) The hot metal pretreatment method according to the above (1) or (2), wherein the blowing of the flux is started after the blowing of the carbon source is completed.

(4) The hot metal pretreatment method according to any one of the above (1) to (3), wherein fluorite is not used during the hot metal pretreatment.

(5) In the hot metal refining method of performing hot metal pretreatment by the hot metal pretreatment method according to any one of the above (1) to (4) and then performing decarburization, the fluorite is used for the decarburization process. A hot metal refining method characterized by not using it. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic view showing a hot metal pretreatment furnace used in the present invention. BEST MODE FOR CARRYING OUT THE INVENTION

For the hot metal pretreatment of the present invention, a refining vessel 1 that can be blown up and down as shown in FIG. 1 is used. The top blowing mainly blows oxygen gas 8 from the tip of the top blowing lance 3 onto the surface of the hot metal. The top-blown oxygen used during the desiliconization reaction can be used as an oxygen source for desiliconization. During the dephosphorization reaction, the upper blowing is used to increase the oxygen potential of the slag to prevent re-phosphorus, and to supplement the heat dissipated to control the temperature to a predetermined temperature.

The bottom blowing is performed using a bottom blowing nozzle 2 provided at the bottom of the purification vessel 1. In addition to having the function of stirring hot metal by injecting a gas containing oxygen gas or inert gas into the hot metal from this nozzle, it also has the function of blowing flux 9 together with carrier gas 7 from the bottom blow nozzle 2 into the hot metal. Have.

If two top and bottom blown converters are used, one of them can be used for hot metal pretreatment and the other can be used for decarburization. Preliminary treatment is performed in a converter for hot metal pretreatment, and then the hot metal is transferred to a converter for decarburization to perform decarburization.

In the hot metal pretreatment of the present invention, the flux blown into the hot metal together with the carrier gas is one or more of quick lime, limestone, and iron oxide, and is a flux mainly containing a component containing at least iron oxide. The flux used for dephosphorization contains CaO sources such as quicklime and limestone as well as iron oxide. Before starting the dephosphorization flux blowing, a flux containing iron oxide as a main component may be blown as a desiliconization aid. As iron oxide used as a flux component, Various materials such as iron ore, mill scale, and sintering dust can be used.

The desiliconization reaction in the hot metal pretreatment is mainly performed using top-blown gaseous oxygen as the oxygen source. A flux containing iron oxide may be blown together with the carrier gas during the desiliconization reaction and used as an auxiliary oxygen source for desiliconization, but even in that case, only gaseous oxygen is used as the oxygen source at the beginning of the desiliconization. Desiliconization, and do not blow the desiliconization flux.

During the desiliconization reaction of the hot metal pretreatment, a carbon source is blown into the hot metal from the bottom blow nozzle together with the carrier gas. As the carbon source, anthracite powder ゃ coatus powder or the like can be used. Before starting the flux blowing, the carbon source blowing is started. Therefore, there is always a time when the carbon source is blown without blowing the flux. Since the carbon source is injected alone, the problem of dephosphorization obstruction that occurs when the carbon source is injected simultaneously with the dephosphorization flux does not occur.

In the present invention, since the desiliconization reaction is not performed by a solid oxygen source as in the past, but mainly by top-blown gaseous oxygen, the hot metal temperature during and after the desiliconization reaction should be higher than before. I can do it. Therefore, slagging of the injected flux can be promoted, and the dephosphorization reaction during hot metal pretreatment can be significantly promoted.

Here, during the desiliconization reaction, the period in which [Si] in the hot metal is oxidized and the [Si] concentration is decreasing with time. In general, when the hot metal [S i] concentration is reduced to 0.03% by mass, the oxidation rate of [S i] is significantly reduced, and it can be considered that the desiliconization reaction has been completed.

As long as the carbon source injection is started before the flux injection is started, the flux injection start timing may be at any time during the desiliconization reaction. At least at the end of the desiliconization reaction, blow in the flux. Otherwise, the dephosphorization reaction following the desiliconization reaction cannot be performed smoothly. On the other hand, as described in the above (2) of the present invention, it is preferable to start the flux blowing after the [Si] concentration has decreased to 0.15% by mass. After the [Si] concentration has decreased to 0.15% by mass, if there is dephosphorized slag (flux), the dephosphorization reaction proceeds together with the desiliconization reaction, so that the [Si] concentration can be reduced to 0.15% by mass. By starting the flux injection after the decrease, the dephosphorization reaction during the desiliconization reaction can be effectively promoted. The means for determining the [Si] concentration during desiliconization may be determined by estimating the amount of desiliconization from the amount of acid supply and the efficiency of desiliconization reaction based on the initial molten iron [Si] value.

The effect of the present invention can be enjoyed even if there is a time when the carbon source and the flux are simultaneously blown during the desiliconization reaction. However, as described in the above (3) of the present invention, if the blowing of the flux is started after the blowing of the carbon source is completed, the waste of the dephosphorizing flux due to the simultaneous blowing of the dephosphorizing flux and the carbon source is reduced. This is more preferable because it can eliminate the risk of ignition that can be avoided when simultaneously injecting a flux containing iron oxide and a carbon source at the same time.

In the present invention, since the desiliconization is performed using the top-blown gaseous oxygen, the hot metal temperature after the desiliconization reaction is high and the slag of the dephosphorized slag is good, so that the subsequent dephosphorization reaction proceeds well. At the same time, since the carbon source is blown, the heat tolerance of refining can be increased, so that the hot metal temperature at the end of dephosphorization after hot metal pretreatment can be lowered. By lowering the hot metal temperature at the end of dephosphorization, it is possible to improve dephosphorization ability by preventing rephosphorization. As described above, since the present invention works favorably for dephosphorization in hot metal pretreatment, as described in (4) of the present invention, a predetermined dephosphorization reaction is performed without using fluorite for hot metal pretreatment. 2/10108

In the present invention, since the dephosphorization ability in the hot metal pretreatment is excellent, it is not necessary to perform an additional dephosphorization treatment in the decarburization treatment. Therefore, as described in the above (5) of the present invention, it becomes possible to reduce the phosphorus concentration in the molten steel to a predetermined concentration without using fluorite for the decarburization treatment.

In the present invention, since the carbon source is added during the hot metal pretreatment to improve the heat tolerance of refining, it is possible to increase the charging ratio of the cold iron source such as scrap, In the coal treatment, Mn ore can be added to replace expensive Mn alloy iron. Furthermore, since there is no need to form dephosphorized slag in the decarburization treatment and the amount of slag is small, it is possible to improve the Mn yield of Mn ore. Example

Using two 280-ton top and bottom blown converters, one as a refining vessel 1 for hot metal pretreatment as shown in Fig. 1 and the other as a refining vessel for decarburization Low phosphorus steel was melted.

In the case of top blowing, oxygen gas 8 is blown onto hot metal 5 using top blowing lance 3. For bottom blowing, six double pipe bottom blowing nozzles 2 provided at the bottom of the converter are used, and oxygen gas or inert gas is blown into the hot metal from the inner pipe. From the space between the inner tube and the outer tube, a hydrocarbon gas is blown as a cooling gas when oxygen gas is blown from the inner tube, and an inert gas such as nitrogen is blown when an inert gas is blown from the inner tube. In the hot metal pretreatment furnace, the flux 9 stored in the flux hopper 4 can be blown together with the carrier gas 7 from the bottom blowing tuyere 2. As the flux 9, a carbon source 9c, quicklime 9a, and sintered dust 9b are used. At this time, an inert gas is used as the carrier gas 7 FC (Fixed Carbon (fixed carbon in coal)) = 80% by mass, VM (Vola tile Matter (volatile matter in coal)) = 6% by mass, Si0 using ₂ = 6.7 wt% anthracite. As the flux to be blown in the same way, a mixture of quicklime powder 9a and sintered dust 9b in a mass ratio of 1: 1 or sintered dust 9b alone was used. The composition of the sintered Dust, T.Fe = 46.7 wt%, CaO = 6 mass ⁰ /. , A1 ₂ 0 ₃ = 2.5 wt%, and the Si0 ₂ = 5.2 mass%. The particle size of the blowing material was set to 1.5ηπη or less. The top blowing during the degassing reaction time increased the oxygen potential of the slag 6 to prevent reversion, and set the flow rate so as to compensate for the heat dissipated and control the temperature to a predetermined temperature.

Table 1 shows the injection status of the flux of carbon source and flux mainly in the pretreatment in each example. Table 2 shows the detailed basic unit, component and temperature results for each example. Examples 1 and 2 of the present invention are examples to which the present invention is applied, and Comparative Examples 1 to 4 are examples using the conventional technology.

〔table 1〕

Pretreatment furnace Decarburization furnace Desiliconization period Dephosphorization period End temperature

Example of the present invention Pulverized coal injection CaO + sintered dust Normal Carbon material added

1 Blowing None Example of the present invention [Si] 0.15% or less [Si] 0.15% or more Normal Carbon material added

2 Pulverized coal injection Ca0 + sintering dust injection None Comparative Example 1 Charcoal CaO + sintering dust Normal Carbon material added

Comparative Example 2 Sintered dust injected Ca0 + Sintered dust Normally carbon material added Injection (added above lump) Comparative Example 3 Fluxes Fluxes Normally carbonaceous material added No blown None Comparative Example 4 Fluxes Fluxes Finish temperature Carbon material added No blowing No blowing Up None

(Table 2)

Inventive invention Inventive comparative example Comparative example Comparative example Comparative example Example 1 Example 2 1 2 3 4 Pre-hot metal (t / ch) 282 279 280 283 280 278 278 Equipment Initial temperature C) 1301 1302 1299 1300 1300 1301 Treatment Initial (C) (Mass%) 4.59 4.61 4.62 4.63 4.59 4.58 Initial stage [P] (mass./.) 0.101 0.102 0.100 0.102 0.100 0.101 Furnace Basic unit of coal (kg / t) 7.1 3.6 7.1 0 0 0 Pulverized coal injection time (min) 4 2 Four

Ca0 + Sintered dust 17.8 17.8 17.8 17.8 0 0 Basic unit (kg / t)

CaO upper charging 5.9 5.9 5.9 5.9 13.9 13.9 Basic unit (kg / t)

Top blowing oxygen 15.8 15.8 15.0 15.0 17.0 17.0 Basic unit (Nm ³ / t)

Total treatment time (min) 14 14 14 14 14 14 Temperature after treatment (° C) 1339 1341 1342 1339 1340 1370 After treatment [C] (% by mass) 4.03 3.87 4.01 3.42 3.41 3.39 After treatment [P] (% by mass) 0.012 0.010 '0.018 0.016 0.020 0.025

Addition of CaF ₂ None None None None None None De-initialized [C] (% by mass) 4.03 3.87 4.01 3.42 3.41 3.39 Charcoal initial [Mn] (% by mass) 0.100 0.101 0.097 0.102 0.101 0.098 Furnace Basic unit of carbon material (kg / t) 0 0 0 14.2 0 0 Sladaborg Yum 20 20 30 35 40 40

Mn ore intensity ( _kg / t) 10 10 10 10 0 5 Blow-off Temp. (.C) 1689 1684 1687 1690 1688 1683 Blow-off [C] (% by mass) 0.451 0.448 0.450 0.449 0.448 0.447 Blow-off [P] (Mass ⁰ /.) 0.012 0.010 0.012 0.011 0.012 0.013 Blow [Mn] (mass%) 0.384 0.381 0.305 0.282 0.100 0.178

Mn yield (%) 71 70 52 45 40

CaF ₂ basic unit (kg / t) None None 2 2 5 5 The end temperature of the pretreatment was set to 1340 ° C except for Comparative Example 4, and the target of 1370 ° C was increased by 30 ° C only in Comparative Example 4. Adjustment of the pretreatment end temperature was performed by adjusting the unit consumption of iron ore charged upward during the pretreatment. However, if iron ore is introduced before or immediately after the start of the dephosphorization reaction, the slag formation of the dephosphorized slag will occur due to a drop in hot metal temperature, so iron iron ore should be introduced as late as possible in the dephosphorization reaction. good. In the decarburization treatment, if heat tolerance exists, Mn ore was added to reduce the unit consumption of Mn alloy iron.

In Example 1 of the present invention, desiliconization was performed only by the upwardly blown oxygen during the desiliconization reaction time, while a carbon source was blown over the entire desiliconization reaction time. At the time of the dephosphorization reaction, quicklime powder and a sinter dust mixture were blown in as fluxes for dephosphorization. In Invention Example 2, the blowing of the carbon source was completed before the [S i] concentration was reduced to 0.15% by mass, and the dephosphorization was completed after the [S i] concentration was reduced to 0.15% by mass. Until then, quicklime powder and a sinter dust compounding agent were injected. The other conditions are the same as in Example 1 of the present invention.

In Comparative Example 1, a carbon source and a sintering dust were blown from the bottom during the desiliconization reaction, and both the top-blown oxygen and the sintering dust were used as the desiliconization oxygen source. At the time of the dephosphorization reaction, quicklime powder and a sintering dust mix were blown in as flux for dephosphorization. In Comparative Example 2, the carbon source was not injected during the desiliconization reaction time of the hot metal pretreatment, but instead lump anthracite was injected from above during the decarburization treatment. Here, it is thought that if the carbon source is supplied by blowing from the bottom blow nozzle during the decarburization process, the blow-off temperature during the decarburization process becomes high, and the life of the bottom blow nozzle will be short and the cost will increase. Therefore, the upward injection of anthracite was adopted. In order to increase the amount of hot metal (C) equivalent to that in Example 1 and Comparative Example 1, it was necessary to use twice as much carbon unit as the unit used in the injection method. Was needed. Other conditions are the same as in Comparative Example 1. In Comparative Example 3, flux was not injected during the hot metal pretreatment, and desiliconization was performed using only the upper-blown oxygen as the oxygen source. At the start of the pretreatment, quick lime was charged upward to form dephosphorized slag. In Comparative Example 4, the pretreatment end temperature was 30. It is the same as Comparative Example 3 except that the target of 1370 ° C at the end of C was set.

First, the phenomenon at the desiliconization reaction time is compared between the inventive example 1 and the comparative examples 1 and 2.

In Comparative Example 2, oxygen gas top blowing and sinter dust blowing were performed during the desiliconization reaction. The iron oxide in the blown sinter dust oxidizes [S i] in the hot metal and also partially oxidizes [C] in the hot metal to form CO gas. All reactions with iron oxide are endothermic reactions and lower the hot metal temperature at the end of the desiliconization reaction. It also lowers the [C] concentration in the hot metal.

In Comparative Example 1, as in Comparative Example 2, [S i] and [C] in the hot metal reacted with the iron oxide in the sintered dust, and this was an endothermic reaction. In Comparative Example 1, since a carbon source was blown during the desiliconization reaction, [C] in the hot metal was always kept saturated. Since the reaction between [C] and iron oxide proceeds as the [C] concentration increases, the reaction between [C] and iron oxide proceeds more than in Comparative Example 2, and the degree of temperature decrease during the desiliconization reaction Becomes larger. Further, since the molten iron (C) is kept in saturation, easily reducing the Fe O in the slag, since Fe O concentration is lower S i 0 ₂ Li Tutsi of FeO _ S i 0 ₂ slag, A phenomenon also occurs in which the melting point of the slag rises and the slag slag property is impaired.

In Example 1 of the present invention, the desiliconization reaction is performed using only the top-blown oxygen gas without blowing sintering dust during the desiliconization reaction time. Since the reaction between the hot metal [Si] and the oxygen gas is an exothermic reaction, the calorific value is larger than in Comparative Examples 1 and 2, and the hot metal temperature at the end of the desiliconization reaction can be increased. carbon The fact that [C] is kept saturated by the source injection makes it easy to reduce FeO in the slag as in Comparative Example 1. can be FeO production amount by many, to retain the slag FeO -Si 0 ₂ slag of low melting point. For the above reasons, in Example 1 of the present invention, the slag at the end of the desiliconization reaction can be made into a slag with good slagging, and the subsequent degassing reaction can advantageously proceed. .

Next, the dephosphorization status of each embodiment will be described.

In Example 1 of the present invention, at the time of the desiliconization reaction, since the desiliconization reaction is performed only with the top-blown oxygen without blowing the iron oxide-based flux, the hot metal temperature at the start of the dephosphorization reaction is high. Furthermore, since the dephosphorization flux added during the dephosphorization reaction is blown into the hot metal together with the carrier gas instead of being injected upward, the synergistic effect with the hot metal temperature gap makes it unnecessary to use fluorite. A dephosphorization reaction can proceed. Also, since the carbon source injection and the dephosphorization flux injection are performed at different times, the injected carbon source does not inhibit dephosphorization. In addition, the temperature at the end of the hot metal pretreatment was kept at 1339 ° C, so that the [P] concentration after the treatment could be reduced to 0.012% by mass. For this reason, it is not necessary to perform additional dephosphorization in the subsequent decarburization treatment, but decarburization treatment was performed by generating 20 kg / t slag to reduce dust. Since fluorite was not added, there was no concern about elution of fluorine from the slag, and the slag could be effectively used. [Carbon source blowing was completed before the [Si] concentration dropped to 0.15% by mass, and dephosphorizing flux blowing was started. This makes it possible for the dephosphorization reaction to proceed even in the latter half of the desiliconization reaction. Was able to accelerate the dephosphorization reaction. As a result, it was possible to reduce the [P] concentration to 0.010% by mass after the pretreatment. On the other hand, because the carbon source injection time was short, the carbon source injection unit remained at 1 Z2 in Example 1 of the present invention.

In Comparative Example 1, since the sintering dust was blown and used as the oxygen source for desiliconization, the hot metal temperature at the start of dephosphorization could not be sufficiently increased, and the (P The concentration decreased only to 0.018% by mass. Therefore, the amount of slag during decarburization and 30k _g Z t, was further fluorite 2 kg / t added to additional dephosphorization treatment.

In Comparative Example 2, since the carbon source was not blown during desiliconization in comparison with Comparative Example 1, the [P] concentration after the pretreatment was 0.016% by mass, which was slightly better than Comparative Example 1. . Because the carbon source is not injected, the oxygen potential can be increased. On the other hand, there are S i0 ₂ Inpu' bets from anthracite was introduced by decarburization. Therefore, it was necessary to increase the amount of slag to 35 kg / t for the slag basicity secure.

In Comparative Example 3, since the dephosphorization flux was not added but added upward, the concentration of [P] decreased only to 0.002% by mass after the pretreatment. Therefore, in the decarburization treatment, slag of 40 kgZt was formed, and fluorite was added at 5 kg / t to perform additional dephosphorization treatment.

In Comparative Example 4, since the temperature after the pretreatment was set to 1370 ° C., which was higher than that in Comparative Example 3, the [P] concentration after the pretreatment reached the highest value of 0.025% by mass. Therefore, slag of 40 kg / t was formed in the decarburization process, and 5 kg / t of fluorite was added to perform additional dephosphorization. The improvement of the heat tolerance of each example and the results of Mn ore addition are compared. In Examples 1 and 2 of the present invention and Comparative Examples 1 and 2, the heat tolerance was improved as a result of adding a carbon source in the hot metal pretreatment or decarburization treatment, and Mn ore was charged at 10 kg / t in the decarburization treatment. Reduction of Mn alloy iron I was able to. In Examples 1 and 2 of the present invention, the amount of slag formed during the decarburization treatment could be minimized, so that the Mn yield of the Mn ore could be improved to about 70%.

On the other hand, in Comparative Example 3, since the carbon source was not added, the heat tolerance was insufficient and Mn ore could not be added. In Comparative Example 4, although the pre-treatment end temperature was raised to improve the heat tolerance, the heat tolerance decreased due to the large amount of slag generated in the decarburization treatment, and the Mn ore was reduced to 5 kg / min. Only t could be added.

In summary, in Examples 1 and 2 of the present invention, a solid oxygen source was not used for desiliconization, and a flux blown into hot metal was used for dephosphorization, so that a high dephosphorization capacity was achieved in the pretreatment. I was able to. In addition, since the carbon source is blown into the separate timing before the dephosphorization flux is blown during the desiliconization, carbon is added to the hot metal at a high yield without impairing the dephosphorization ability, and the heat tolerance of refining Could be increased.

Under the conditions of Example 1 and Comparative Example 3, continuous operation was performed for each of 20 channels, and the amount of refractory erosion was compared. As a result, it was confirmed that in Example 1, which did not use fluorite, the amount of erosion loss of the decarburization furnace refractories was 30% less than that of Comparative Example 2, which used 5 kg / t of fluorite in the decarburization furnace. It helped to reduce refractory costs. Industrial applicability

The present invention relates to a hot metal refining method in which decarburization is performed after hot metal pretreatment in which desiliconization and dephosphorization is performed using a top and bottom blown refining vessel. However, during the desiliconization reaction, a carbon source is blown into the hot metal and then a dephosphorizing flux is blown, so that carbon can be added to the hot metal at a high yield to increase the heat tolerance of refining. Sa Furthermore, a high dephosphorization ability can be realized in the pretreatment. In the present invention, if the degassing flux is started after the [Si] concentration has dropped to 0.15% by mass, the dephosphorization reaction can be caused even during the desiliconization reaction, and The ability to remove phosphorus can be improved.

The present invention is to increase the thermal tolerance of refining by adding carbon into hot metal at a high yield without impairing the dephosphorization ability by starting the dephosphorization flux injection after the carbon source injection. And the risk of ignition can be avoided.

As a result of improving the dephosphorization performance in the hot metal pretreatment, the present invention is to perform the purification without using the fluorite in the hot metal pretreatment and without using the fluorite even in the decarburization process. Becomes possible. Thereby, the amount of refractory erosion can be reduced and the cost of refractory can be reduced.

Claims

The scope of the claims

1. Using a refining vessel capable of being blown from the bottom to the top, de-siliconize the hot metal by injecting into the hot metal a flux that is one or more of quick lime, limestone, and iron oxide and contains at least a component containing iron oxide. A hot metal pretreatment method for dephosphorizing, wherein a carbon source is blown into the hot metal during the desiliconization reaction, and the carbon source blowing is started before the flux blowing is started.

2. The hot metal pretreatment method according to claim 1, wherein the flux blowing is started after the [Si] concentration has decreased to 0.15% by mass.

3. The hot metal pretreatment method according to claim 1, wherein the blowing of the flux is started after the blowing of the carbon source is completed.

4. The pretreatment method for hot metal according to any one of claims 1 to 3, wherein fluorite is not used at the time of pretreatment of hot metal.

5. A method for refining hot metal, which comprises performing a hot metal pretreatment by the hot metal pretreatment method according to any one of claims 1 to 4 and then performing a decarburization process. A hot metal refining method characterized by using no iron.