JP5477704B2 - Hot metal dephosphorization method - Google Patents

Description

  The present invention provides a hot metal dephosphorization and dephosphorization method capable of providing both a low phosphorus steel material having excellent characteristics and a stable slag by-product without using an F source. In the present specification and claims, “%” represents “% by mass” unless otherwise specified.

In recent years, there has been an increasing need to reduce CO ₂ emissions in order to suppress global warming caused by carbon dioxide, etc. In steel materials, for example, steel materials for automobiles, high strength and workability have been achieved to reduce weight. Development of steel plate materials that satisfy both requirements is demanded.

In order to produce such a high-performance steel material, it is basically required to reduce impurities such as phosphorus and sulfur contained in the steel material. Since the 1980s, technology for dephosphorization and desulfurization treatment has been developed in the preliminary treatment process in the hot metal stage, and in recent years, it has been widely spread in blast furnace integrated steelworks. In the dephosphorization and desulfurization treatment of these mass-produced steels, reduction of refining costs is also an important issue, and inexpensive and stably available CaO-based fluxes are used as refining agents. However, since CaO itself is an oxide with a high melting point and does not melt and form slag with high dephosphorization and desulfurization capacity, fluorite containing CaF ₂ as the main component has been conventionally used as a flux. . That is, by using slag as a liquid, the slag droplets are entrained in the hot metal or the hot metal droplets are entrained in the slag under vigorous stirring, and the reaction rate is increased by significantly increasing the reaction interface area. Therefore, processing on an industrial scale was made possible. However, F becomes the elution regulated substances from the soil in the soil environment standard, because the steel slag as civil engineering materials to be regulated in the F elution, it becomes impossible to effect, using CaF _2. Therefore, various methods have been proposed for causing CaO to effectively act on dephosphorization and desulfurization reactions without using a halide such as CaF ₂ .

  In steelmaking slag, it has been found that phosphorus is finally present in the solid solution of calcium phosphate or calcium phosphate and dicalcium silicate. For this reason, attempts have been made to positively utilize these solids in which phosphorus is dissolved during the refining reaction. However, in this method, the slag is in a mixed phase of solid and liquid, the phenomenon is complicated, and the basic part such as how the phosphorus is fixed by the mechanism has not been elucidated, and research has been actively conducted.

As a dephosphorization method using a dephosphorization agent not containing F, Japanese Patent Application Laid-Open No. 11-173244 discloses a method of supplying gaseous oxygen before supplying a CaO source, and a solid oxygen before supplying a CaO source. Supplying a source is disclosed. This is based on the idea that in order to produce liquid phase slag while CaF ₂ cannot be used, FeO is produced at an early stage, FeO rich slag is produced at an early stage, and CaO is contained therein. It seems to be based on the idea of melting. However, according to the study by the inventors, when oxygen gas is supplied, preferential oxidation of silicon proceeds when the silicon concentration in the hot metal is high, so that the FeO melt is not sufficiently formed, and it is halfway. It was found that when a large amount of FeO was generated, coalescence between CaO sources and sintering were promoted, and as a result, slag rapidly lost fluidity and did not contribute to dephosphorization. Moreover, even when an iron oxide source was added, it turned out that an effect | action is inadequate depending on the apparent density and particle size. In view of the context, the present disclosure is considered to have been disclosed particularly for low silicon concentration hot metal that has been subjected to pre-silicon removal treatment. On the other hand, as will be described later, the present invention has a great effect on hot metal having a high silicon concentration in which pre-silicon removal treatment is not performed.

A similar disclosure can be found in Japanese Patent Application Laid-Open No. 2002-161304. That is, a method is disclosed in which the oxygen source is added before the CaO source is added to increase the FeO concentration in the slag, and then the CaO source is added. However, as will be described later, in order to secure FeO necessary for the dephosphorylation reaction and the hatching reaction of the CaO source, it is particularly necessary to simply spray gaseous oxygen or add an iron oxide source, in order to ensure the pre-treatment silicon. It became clear that it was insufficient when the concentration was high or when it was desired to perform a short-time treatment. That is, it is important to produce a large amount of molten slag with a high FeO concentration at an early stage, but when the specific gravity of the iron oxide source is small or the particle size is too small, the slag layer in the foamed state It was clarified that there was a case in which slag remained in the unreacted state because it could not settle inside and did not easily reach the high temperature slag-hot metal interface. In addition, if the addition of the CaO source is delayed, then the addition capacity of the CaO source is insufficient and the time required to add the predetermined CaO source becomes longer, the processing cycle time becomes insufficient, or the CaO source is added at high speed. Therefore, when the amount of the liquid slag is small, it is not preferable because it is agglomerated and coalesced to form a slag having poor reactivity, and the dephosphorization efficiency may be lowered. In particular, when the concentration of silicon in the hot metal is high, the amount of CaO necessary for ensuring basicity increases according to SiO ₂ generated by the desiliconization reaction, resulting in a problem that the cycle time is insufficient. In this regard, in the present invention, such a CaO is produced by promptly generating liquid FeO by quickly bringing the solid oxygen source to the slag-molten metal interface and capable of forming molten FeO quickly. An efficient desiliconization and dephosphorization treatment of undesiliconized hot metal was made possible without imposing restrictions on the addition rate, that is, without increasing the processing cycle time. On the other hand, the publication also mentions that the use of gaseous oxygen to secure FeO before adding the CaO source, but as will be described later, the production rate of FeO is sufficient with gaseous oxygen. Rather, it is inappropriate for the purposes of the present invention.

Japanese Unexamined Patent Application Publication No. 2009-114494 is disclosed as a technique for achieving both efficient dephosphorization treatment and stabilization of discharged slag. In the same publication, claim 1 describes that 75% or more of quicklime to be used is powdered and sprayed onto the hot metal bath surface from a top blowing lance together with a gaseous oxygen source, and slag basicity (% CaO) after dephosphorization treatment. / (% SiO ₂ ) is set to 2.3 or more and 3.5 or less, and the Al ₂ O ₃ concentration is set to 5 to 10%. However, Al ₂ O ₃ is known to be a component that promotes slag foaming, especially when the furnace volume is small, slag and hot metal overflow from the furnace port, so-called slopping becomes intense, Processing is forced to stop, making stable operation difficult. Further, fine powder CaO may also deteriorate the dephosphorization efficiency depending on the use conditions, and it is necessary to limit it as in the present disclosure condition.
As described above, efforts have been made to improve the efficiency of the dephosphorylation reaction without using the F source, but the studies so far have mainly focused on the CaO source particle size, the addition conditions, or the conditions for blowing gaseous oxygen. Although there are a number of disclosures, what has been described regarding the method of using the oxygen source is described above in JP-A-2002-161304, it depends on the type of solid oxygen source, the particle size, or its control. There are no disclosure examples referring to the effects.

Japanese Patent Laid-Open No. 11-173244 JP 2002-161304 JP JP 2009-114494 A

The present invention is an inexpensive and efficient dephosphorization method without using a halogen source such as CaF _{2 in} a method of performing desiliconization and dephosphorization treatment of hot metal without using pre-desiliconization treatment of hot metal as a main raw material. It is an object to establish a technique for processing.

The present invention made to solve the above problems is a method for desiliconization and dephosphorization of hot metal in which a solid oxygen source and a CaO source are added to hot metal having a silicon concentration of 0.20% or more, and dephosphorization is performed following desiliconization. a is, the particle diameter of the solid oxygen source to be added, 0.003 m or more to less than 0.03 m, and an apparent density of the particles 3000 kg / m ³ or more, decarburization slag added from the initial as CaO source, the hot metal in the silicon concentration Is reduced to 0.05% or less, and then a CaO source having a particle size of 1 mm or less is added .

The hot metal dephosphorization reaction is a reaction in which phosphorus oxidized by an oxygen source such as oxygen gas or FeO is fixed by CaO. In order to increase the speed, a large amount of CaF ₂ has been used in the past to generate liquid slag with high fluidity and high basicity, facilitating transfer of phosphorus from hot metal to slag, Dephosphorization treatment was performed in time. However, it is the F elution from the soil is regulated by law, such as the steel slag roadbed material, when utilized in civil engineering is to develop a method without using CaF ₂ is dephosphorization sufficiently proceed It became a problem. On the other hand, FeO itself melts together with CaO to form a low-melting slag, so it is better known than before that producing a large amount of FeO is effective for forming CaO as a liquid phase slag. It has been. However, when processing the non-desiliconized hot metal as in the case of the present invention, in the initial stage where the silicon concentration in the hot metal is high, FeO is consumed in the oxidation of silicon, so it is difficult to ensure the amount of molten FeO, Moreover, since the SiO ₂ concentration in the slag increases, the FeO concentration relatively decreases. Furthermore, when CaO is present, calcium silicate 2CaO · SiO ₂ is produced, but 2CaO · SiO ₂ itself has a high melting point of 2100 ° C or higher, so the surface of CaO is solid at a hot metal pretreatment temperature of about 1300 to 1400 ° C. And will prevent further dissolution of CaO. Therefore, it is necessary to consider the balance between the addition of the CaO source and an appropriate rate at which 2CaO · SiO ₂ is not generated, that is, the generation rate of SiO ₂ .

  When fine powder CaO is added here as a CaO source, small particles agglomerate and coalesce due to the capillary effect of a small amount of liquid FeO, and CaO and FeO trapped in it do not come into contact with hot metal and are effective. Dephosphorization efficiency deteriorates without acting. Increasing liquid FeO is important to avoid condensation of CaO particles. Therefore, in such a situation where the initial hot metal temperature is low and even if oxygen is added, the desiliconization reaction is prioritized and liquid FeO is difficult to generate, it is possible to add a CaO source having a large particle size rather than fine powder CaO. It is important in hindering the progress of agglomeration and sintering reactions. That is, the capillary pressure acting between the particles due to the liquid existing between the particles acts more strongly as the particle size becomes smaller. However, if pure CaO with a large particle size is added, melting will not be completed by the end of dephosphorization, so using decarburized soot reduces the amount of unreacted CaO in the slag and is effective for decarburizing soot. Convenient in terms of use.

The reason why the apparent density of the solid oxidation source is 3000 kg / m ³ or more and the particle size is 0.003 m or more in the present invention will be described below. As a result of detailed analysis by the inventors of the present application, even when the iron oxide source is added to the furnace, if the specific gravity is small, the inside of the formed slag layer settles and is the progressing site of the reaction. In some cases, it takes a long time to reach the slag-hot metal interface, and it takes a long time to become molten FeO, and in some cases, it may not contribute at all to the reaction while floating on the slag surface. I found. Until now, such a phenomenon has been generally ignored, and it has been considered that the added auxiliary material exhibits its effect immediately except for the CaO source. As described in paragraph 0010, the lack of FeO at the slag-hot metal interface becomes more prominent in the initial stage of treating the non-desiliconized hot metal, which has a high silicon concentration in the hot metal, and more particularly, It is necessary to quickly settle in the slag layer to reach the interface. In general, solid particles in a gas or liquid settle or float at a speed determined by the specific gravity difference from the surrounding fluid, the viscosity of the fluid, and the particle diameter. In the case of spherical particles existing in a uniform fluid, this settles or flies at a speed determined by Stokes' law in equation (2).
v _t = D _p ² (ρ _p -ρ) g / 18 η (1)
Where, v _t : terminal velocity (m / s), D _p : particle size (m), ρ _p : particle apparent density (kg / m ³ ), ρ: slag apparent density (kg / m ³ ), η: Viscosity coefficient of slag (Pa · s), g: Gravitational acceleration (m / s ² )
Here, the apparent density is obtained by dividing the weight of the particle by the volume including pores existing inside the particle, and is not a true density. The reason why the apparent density is used as an index is that, in the equation (1), the sedimentation speed is determined by the apparent density, not the true density evaluated excluding the pores.
However, in the formula (1), the downward speed is positive. In the case of a shape other than a sphere, Dp represents a sphere equivalent diameter.

  In general, the viscosity of slag is higher than that of ordinary liquids and is higher at lower temperatures. Therefore, it seems to be very high under low temperature conditions in the initial stage of desiliconization and dephosphorization. In the actual slag, CO gas generated by the reaction between hot metal and FeO in the slag is generated at the slag-hot metal interface and is bubbling, and entrainment of hot metal droplets is also occurring, so the slag is a uniform liquid Rather, the equation (1) cannot simply be applied to the velocity of solid particles that settle in it. The phenomenon is complicated when solid particles settle in a foamed liquid.

In fact, if the solid oxygen source is 3000 kg / m ³ or more and the particle size is 0.003 m or more, it will settle in the slag layer within 2 minutes, so that it will reach the hot metal surface and the temperature will rise. And contribute to the reaction. However, if the particle size is 0.03 m or more, the heat transfer to the inside becomes the rate of melting, which is not preferable. In addition, when a large lump is in direct contact with the hot metal, a rapid decarburization reaction occurs, causing slopping, and is not preferable because it does not melt in a short time. Therefore, the particle size is desirably less than 0.03 m.

  On the other hand, a gaseous oxygen source is also used in the hot metal dephosphorization treatment, but particularly when the silicon concentration is as high as 0.2% or more, the generation of FeO is not sufficient by the gaseous oxygen top blowing method. This is because when the reaction interface between gaseous oxygen and hot metal is hot, the decarburization reaction rate is large, and the oxygen used to produce FeO is insufficient compared to the solid oxygen source and when the silicon concentration is high. Is more difficult to produce FeO because it is used for desiliconization reaction.

  Here, as soon as liquid FeO is formed by adding a solid oxygen source, as described above, slopping becomes intense and stable operation becomes difficult in some cases, so in order to suppress foaming of slag. It is desirable to increase the basicity by adding a CaO source with good hatchability from the beginning. However, in this case, as described in paragraph 0010, when the CaO source has a small particle size, it is agglomerated and coalesced by the capillary action of the liquid phase in the initial stage of processing, particularly at a low temperature and a high slag viscosity. Therefore, the purpose of this is to recycle the slag generated in the converter, which is a process of converting the hot metal into steel, after cooling and solidifying in the yard, and then collecting the bullion and recovering the metal. The cost is also low and it is very convenient. The melting point is relatively low at about 1400 ° C., and a particle size of about 0.005 to 0.025 m can be used.

  However, when the silicon concentration in the hot metal is 0.05% or less and the desiliconization reaction is completed, the decarburization reaction rate increases and the CO gas generation rate increases. It is desirable to add a CaO source having a particle size of 1 mm or less in order to increase it quickly. By doing so, a calcium silicate phase is crystallized, in which phosphoric acid in which slag has already been taken in is solid-solved and is stably fixed, and the liquid phase rate of slag is lowered and forming is suppressed. The timing of starting the addition is added after the desiliconization reaction is completed, that is, when the silicon concentration becomes 0.05% or less. If it is added before this time, the temperature has not risen sufficiently, so liquid slag and fine powder coexist, and the slag solidifies due to the capillary effect of the liquid, and CaO is trapped in the particles to remove phosphorus. It is not preferable because it does not contribute to the above.

  In addition, to add a CaO source with a particle size of 1 mm or less, simply dropping it from above causes it to be blown off outside the furnace by riding on an air current, so it blows into the hot metal from the bottom blowing tuyere or lance, or It is a desirable method to prevent scattering by spraying the hot metal surface from the blowing lance and surely reach the slag-hot metal interface.

  As described above, according to the present invention, FeO acts effectively from the initial stage of desiliconization and dephosphorization, and the dephosphorization reaction proceeds promptly in the desiliconization and dephosphorization treatment. Moreover, since phosphorus is dissolved in the calcium silicate solid phase after completion of the desiliconization reaction, dephosphorization proceeds promptly until the end of the treatment. Furthermore, since slopping is also suppressed, it is possible to omit the prior desiliconization process and perform an efficient desiliconization and dephosphorization process in a short time.

It is a cross-sectional view of a hot metal dephosphorization furnace suitable for carrying out the present invention.

  FIG. 1 shows an example of an optimum equipment configuration for carrying out the present invention. It comprises a hot metal dephosphorization furnace 1 and a decarburization furnace, each comprising a converter type furnace equipped with an upper blowing lance for supplying oxygen gas. The decarburized soot produced by decarburization blowing in the decarburization furnace is partially left in the furnace, the rest is discharged into a slag pan, and once cooled and solidified, it is crushed in the crushing step. The metal is removed in the magnetic separation process. Thereafter, crushing and sieving are performed as necessary. Thereafter, it is used in a hot metal dephosphorization furnace.

  When a CaO source having a particle size of 1 mm or less is further added in the dephosphorization furnace, it is desirable to add powdery dephosphorization agents 11 and 13 from the top blowing lance 5 or the bottom blowing nozzle 8. By doing in this way, scattering can be prevented and it can supply steadily to a hot metal-slag interface.

Table 1 shows examples according to the present invention together with comparative examples.
In the converter type hot metal pretreatment furnace, 30 tons of scrap was charged, and 2270 tons of hot metal was charged. Supply of oxygen gas 6 from the top blowing lance 5 was started. At the same time, the solid oxygen source and decarburization soot were continuously added from above. Addition of both solid oxygen source and decarburized soot was completed before the silicon concentration dropped below 0.05%. Subsequently, the powdered dephosphorizing agent 13 was sprayed onto the hot metal surface from the top blowing lance 5 and continued until the treatment was completed. After elapse of a predetermined time, the top blowing oxygen gas was stopped, the furnace was tilted, and hot metal was poured out into the ladle from the tap hole 15.
In Example 1, as the solid oxygen source, the converter dust, which is a by-product in the steel making process, was granulated and then fired to increase the apparent density to 3760 kg / m ³ and the particle size was 5 to 15 mm. . As a CaO source for dephosphorization, decarburized soot whose composition is shown in Table 3 was used at a rate of 17.3 kg / t (where t represents the total tonnage of hot metal + scrap, the same applies hereinafter). Furthermore, 14.0 kg / t of fine powder CaO of 1 mm or less was supplied from the main lance. The phosphorus concentration after dephosphorization was a sufficiently low value of 0.015%.

Table 2 shows Example 2 together with a comparative example.
In Example 2, iron ore having a large apparent density was used as a solid oxygen source, decarburized soot and 1 mm or less fine powder CaO were used as a CaO source. Scrap 3550t was charged into the hot metal pretreatment furnace 1, and further hot metal 2251t was charged. Thereafter, the oxygen gas 6 starts to be blown up through the main lance 5, and the upper addition of the solid oxygen source and the decarburized soot is started from the furnace hopper 4, and the upper addition has a Si concentration of 0.05% or less in the hot metal. Finished until. Subsequently, spraying of 1 mm or less of CaO through the main lance 6 was started and continuously added until the end of the treatment. Thereafter, hot metal was poured into the ladle from the steel outlet hole 15. The phosphorus concentration in the hot metal was very good, 0.009%.

(Comparative example)
On the other hand, the dephosphorization efficiency of the comparative example was inferior to that of the example. In Comparative Example 1, dust pellets were used, but since they were produced by the rolling granulation method, the porosity was high and the apparent density was low. Treatment was carried out under substantially the same conditions as in Example 1, but phosphorus was reduced only to 0.038%. In Comparative Example 2, iron ore having a large apparent specific gravity was used as the solid oxygen source, but since powder with a particle size of about 2 mm was used, it was presumed that it did not settle, and the achieved [% P] was as high as 0.045%. . In Comparative Example 3, the same pellets as in Example 1 were used, but since a large mass having a particle diameter of 42 mm was used, melting and hatching were slow and it was not effective for dephosphorization.
In Comparative Example 4, iron ore having an apparent specific gravity was used as a solid oxygen source, and fine powder CaO of 1 mm or less was added from the beginning. Therefore, the slag solidifies and loses fluidity, and may be compared with Comparative Examples 1 to 3. However, the dephosphorization did not progress so much. In Comparative Example 5, since the slopping was intense and the process was forced to be interrupted, the process took a long time of 15 minutes or more, and a waiting time occurred in the decarburization furnace as the next process, resulting in a decrease in productivity. .

  INDUSTRIAL APPLICABILITY The present invention can be widely applied to steel making methods using hot metal as a raw material and having hot metal dephosphorization and decarburization processes.

DESCRIPTION OF SYMBOLS 1 Hot metal dephosphorization furnace 2 Hot metal 3 Scrap 4 Upper furnace hopper 5 for upper addition of dephosphorization agent Top blowing lance 6 Oxygen gas 7 Dephosphorization agent blowing blow tank 8 Bottom blowing tuyere 9 Nitrogen gas 10 Upper addition dephosphorization agent 11 Desorption Phosphorous agent 12 Dephosphorizer blow tank for top blowing 13 Dephosphorizer 14 Slag 15 Hot water outlet

Claims (1)

A method of desiliconization and dephosphorization of hot metal in which a solid oxygen source and a CaO source are added to hot metal having a silicon concentration of 0.20% or more , followed by dephosphorization treatment, and the particle size of the solid oxygen source to be added is 0.003m or more and less than 0.03 m, and an apparent density of the particles 3000 kg / m ³ or more, the addition of decarburization slag from the initial as CaO source, after dropped to 0.05 percent in the silicon concentration molten iron, the particle size less than 1mm A method for desiliconization and dephosphorization of hot metal, which comprises adding a CaO source .

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