JPS6363601B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a lime-based refining flux for simultaneous dephosphorization and desulfurization treatment of hot metal and a method of using the same, in particular, it easily realizes appropriate preliminary treatment of hot metal, reduces the burden on steelmaking operations in converters, and reduces the amount of slag generated. The aim is to make this possible. Preliminary refining of hot metal is a process in which impurities such as phosphorus and sulfur are removed from hot metal extracted from a blast furnace before it is charged into a converter for oxidation refining. The current ironmaking process involves reducing iron ore with coke in a blast furnace to produce hot metal with a carbon concentration (hereinafter abbreviated as [%C]) of 4.5%, which is then heated in a converter with pure oxygen gas to a specified [%C]. ] The mainstream method is to decarburize to the target steel. Among the impurities in hot metal, silicon (Si) and phosphorus (P) are oxidized in the converter, form slag with quicklime, fluorite, etc. added to the furnace, and are removed. On the other hand, sulfur (S) cannot be removed in a converter with an oxidizing atmosphere, so most steelworks currently do this by adding a refining agent containing quicklime or calcium carbide (CaC ₂ ) to the hot metal. A process is used to remove the waste before charging it into the converter. In recent years, the superiority of a process that removes not only S but also Si and P from hot metal before charging it into a converter has been shown, and many research reports have been published. List the advantages of this process. (1) Since dephosphorization, sulfur, and silicon are completed before charging into the converter, only decarburization needs to be performed in the converter.
The burden of converter operation is reduced. (2) Because the process is carried out at a low temperature that is advantageous for the deP reaction, the deP
It is highly efficient and can reduce the amount of quicklime used. (3) Even if the amount of slag generated from hot metal treatment and subsequent converter blowing is combined, it is less than the amount of slag generated from the current process. (4) Iron loss is reduced by reducing the amount of slag. Moreover, the burden of slag processing is reduced. There are many things that can be mentioned. Refining agents used in hot metal pretreatment are:
It can be roughly divided into two types: one is soda ash-based flux (mainly composed of Na ₂ CO ₃ ), and the other is quicklime-based flux (mainly composed of CaO). The former hot metal treatment process using flux is a well-known method as reported, for example, in "Tetsu to Hagane", Vol. 67, 1981, pp. 323-332. The key point of this method is to first remove Si from hot metal using iron oxide such as iron ore or mill scale, and then simultaneously remove S and P using soda ash. However, not only in this process, but in general, soda ash-based fluxes severely erode the refractory lining of refining vessels, resulting in frequent repairs to the vessels, and because soda ash is a relatively expensive auxiliary material. However, it may be subject to economic constraints and lacks versatility as a flux. On the other hand, since quicklime-based fluxes have been widely used in converters and hot metal desulfurization, there is less problem of corrosion of refractories, and they are far more economically advantageous than soda ash. However, conventional quicklime-based fluxes have the following drawbacks. Generally, as a condition for efficient deP and S removal of hot metal, it is necessary that strong basic oxides (e.g. CaO, Na ₂ O (Na ₂ CO ₃ ), etc.) coexist in both locations. . Further, in the case of deP, an oxidizing atmosphere (in the coexistence with O ₂ gas and iron oxide) is advantageous, whereas in the case of deS, a reducing atmosphere is more advantageous. Therefore, simultaneous deP and S removal cannot be performed efficiently unless under an appropriate atmosphere. In this regard, soda ash-based fluxes have a strong affinity between Na, P, and S in the flux, so the deP reaction progresses even in a weak oxidizing atmosphere, and the deS reaction progresses even in a weak reducing atmosphere. Therefore, simultaneous withdrawal from P,
This means that de-S can be done efficiently. When performing simultaneous deP and deS using a quicklime-based flux, the atmosphere must be delicately adjusted because the affinity between Ca and PS is weaker than that of Na. Conventionally, this method had not been established, so it was difficult to use a quicklime-based flux. No simultaneous deP-deS was used. This invention discloses a method for efficiently performing simultaneous deP and deS refining using quicklime-based flux in a torpedo vehicle, for example, by determining the composition of the refining flux and This paper proposes a new method for using the refined flux. The inventors tried to develop a flux for dephosphorizing hot metal, and when investigating the dephosphorization behavior by injecting various fluxes into the hot metal in a torpedo car, they found that the ratio of CaO to Fe ₂ O ₃ among the flux components We found that withdrawal from S is progressing at the same time as withdrawal from P. As mentioned above, in order to deP from hot metal using a CaO-based flux, it is advantageous to mix a large amount of solid oxygen sources such as iron ore or milkale into the flux, but this is the opposite for deS. disadvantageous to Therefore, when simultaneous deP and S removal is aimed at, an appropriate range naturally exists for the content ratio of the solid oxygen source. The inventors conducted a hot metal treatment experiment using a CaO-based flux using a torpedo vehicle, and determined this appropriate range experimentally. Figure 1 shows a comparison of the S desorption rate constant using the ratio of CaO to Fe ₂ O ₃ as an index of flux composition. The desulfurization rate constant K _s was determined from equation (1), assuming that desulfurization proceeds according to a first-order reaction formula. [%S] = [%S] _i exp (−k _s W _flux )…(1) Here, W _flux is the amount of flux added per ton of hot metal, [%S], [%S] _i are each W _flux (Kg／
t) is the S concentration in the hot metal when the flux is added and the S concentration before treatment. Therefore, the unit of _ks is 1/(Kg/t)=t/Kg. As the CaO content in the flux increases, k _s increases linearly. (In addition, if k _s takes a negative value,
This is because the blast furnace slag on top of the hot metal was not removed during the main hot metal treatment, so S in the slag migrated to the hot metal. ) In other words, in order to advance the S removal reaction, from Figure 1
It is necessary that CaO/Fe ₂ C ₃ is 0.5 or more,
The larger CaO/Fe ₂ O ₃ is 0.5 or more, the more
The S removal rate increases, and efficient S removal becomes possible. Figure 2 shows the relationship between the dephosphorization rate constant k _p and CaO/Fe ₂ O ₃ . k _p is a constant obtained in the same way as k _s , and as is clear from the figure, k _p is a constant that CaO/Fe ₂ O ₃
The maximum value is taken at 0.75. It is thought that the deP reaction by CaO-based flux proceeds according to the formula (2): 3CaO + 5/3Fe ₂ O ₃ + 2 P = 3CaO・P ₂ O ₅ + 10/3Fe...(2), but at this time Fe The stoichiometric ratio of CaO to ₂ O ₃ is 0.63. However, at the same time as deP, the deS reaction of formula (3), CaO+ S = CaS+ O (3), also proceeds, so if CaO used for deS is also taken into account, the stoichiometric ratio becomes 0.72, which is the experiment shown in Figure 2. It is in good agreement with the value. In the dephosphorization reaction, when the CaO/Fe ₂ O ₃ ratio is less than 0.75, the amount of CaO to fix the P ₂ O ₅ of the dephosphorization product is insufficient;
In the above case, it can be explained that since Fe ₂ O ₃ , which is an oxidizing agent for P , is insufficient, the P removal rate reaches its maximum when CaO/Fe ₂ O ₃ =0.75. In order to efficiently remove P and S at the same time, k _s
It is desirable to have a CaO/Fe ₂ O ₃ flux in which both k and k _p take large values, and from Figures 1 and 2, CaO/Fe ₂ O ₃
= 0.75 is optimal, where CaO/Fe ₂ O ₃ 0.90
Then, the k _p value does not become extremely large, and k _s becomes even larger. On the other hand, if CaO/Fe ₂ O ₃ ≧0.6,
It can be seen that there is no practical problem in simultaneous P removal and S removal processing when particularly low [%S] is not required. In the above actual experiment, fluorite, cryolite, or colemanite was added as a solvent, and limestone was added to generate gas to enhance stirring during flux injection. The behavior as already described in the case of flux formulations of 5 to 20% by weight of stone, cryolite, and colemanite alone or in combination of two or more, and for limestone in the range of 10 to 35% by weight. It was confirmed that it represents Regarding limestone, the CaO generated by the CaCO ₃ = CaO + CO ₂ reaction is combined with CaO from quicklime to be CaO/
Calculate the Fe ₂ O ₃ ratio. For solvents, if the content is less than 5% by weight, it will result in poor slag formation, and if it exceeds 20% by weight, there will be severe erosion and damage to refractories, while for limestone, if the content is less than 10% by weight, the amount of CO ₂ generated will decrease. If the amount is insufficient, the effect of strengthening the stirring of hot metal will be insufficient, and if it exceeds 35% by weight, the endothermic effect due to the decomposition of CaCO ₃ will become excessive, resulting in an unfavorable temperature drop of the hot metal. is limited. Therefore, this invention contains quicklime as a main component, 5 to 20% by weight of a solvent selected from fluorite, cryolite, and colemanite, and 10 to 35% by weight of limestone, with the remainder being iron ore, A solid oxygen source such as mill scale with a CaO/Fe ₂ O ₃ ratio of 0.60~
The lime-based refining flux with a blend of 0.90 is used for preliminary refining at the same time as dephosphorization and desulfurization of hot metal, making it possible to effectively extract the fruit. Next, Figure 3 shows the above-mentioned CaO/Fe ₂ O ₃ = 0.60~
Indicates k _p and k _s when 0.90 powdered refined flux is injected into the hot metal inside the torpedo car at different feeding speeds,
Both k _p and k _s decrease at blowing speeds of 400 Kg/min or higher. When the blowing speed is low, the reaction proceeds efficiently, but there are disadvantages such as a longer treatment time and a larger drop in hot metal temperature, so in practice a blowing speed of 100 to 400 kg/min is recommended. It is desirable to supply flux at Figure 4 shows [%Si] and deP of hot metal during pretreatment.
From the same figure, [%Si]<0.25
When [%Si]<0.10, a higher dephosphorization rate is obtained. Therefore, the hot metal [%Si] before deP treatment is preferably 0.25% or less, more preferably [%Si]<0.10. Note that the influence of hot metal [%Si] on S removal is not significant, so there is no need to take it into account. The temperature of the hot metal before the start of treatment is determined from the amount of temperature drop during treatment and the minimum temperature required for the hot metal after treatment. The latter is 1200 to 1250°C, and the former is proportional to the flux consumption unit (amount of flux required to process 1 ton of hot metal, unit: Kg/t pig iron), and is usually 50 to 120°C. Therefore, the minimum temperature of the hot metal before the start of treatment is 1250-1370°C. usually,
When the temperature of hot metal tapped from a blast furnace is measured in a torpedo car, it is 1350 to 1450°C, and if the treatment is started in this temperature range, the deP and deS reaction efficiency will not be particularly reduced. Therefore, when pre-treating hot metal using the deP/S flux of this invention, the hot metal temperature is 1250°C.
Temperatures of up to 1450°C are fine, but if a large amount of flux is to be injected, the temperature drop during treatment will be large, so it may not be possible to process at temperatures below 1300°C within the above range. The temperature is over 1300℃ and there is no problem. Example 1 Contains 5% by weight of fluorite and 10% by weight of limestone,
CaO/Fe ₂ O ₃ = 0.64 using iron ore as Fe ₂ O ₃
The flux was injected into the hot metal inside the torpedo car at a rate of 200 kg/min. Table 1 shows the hot metal components before and after treatment. The amount of hot metal was 183 tons, and the amount of flux injected per ton was 44 kg.

[Table] Example 2 Contains 15% by weight of fluorite, 20% by weight of limestone,
CaO/Fe ₂ O ₃ = 0.75 using iron ore as Fe ₂ O ₃
The flux was injected into 167.2 tons of hot metal inside a torpedo car at a rate of 200 kg/min. Figure 5 shows the relationship between flux consumption and component changes during treatment, and the hot metal components and temperature before and after treatment are shown in Figure 5. Shown in the table.

[Table] In each of the above embodiments, the case of blowing into a torpedo car was shown, but it can also be applied to de-P and de-S of hot metal in a hot metal charging ladle or a hot metal transfer ladle. In this case, if the blowing speed is high, the scattering of slag and metal will increase, so it is necessary to take countermeasures. As described above, according to the present invention, pre-refining of hot metal using quicklime-based flux can be carried out advantageously, particularly in effective simultaneous deP and deS treatment.

[Brief explanation of drawings]

Figure 1 is a graph of the relationship between the CaO/Fe ₂ O ₃ ratio of flux and the desulfurization reaction rate constant, and Figure 2 is a graph of the relationship between the CaO/Fe ₂ O ₃ ratio of flux and the dephosphorization reaction rate constant. Figure 3 is a graph of the relationship between the flux injection rate and the dephosphorization/desulfurization reaction rate constant.
The figure is a graph of the relationship between hot metal [%Si] and dephosphorization rate.
It is a graph showing changes in S][%P].

Claims (1)

[Claims] 1. Quicklime as the main component, 5 to 20% by weight of one or more solvents selected from fluorite, cryolite, and colemanite, and 10% of limestone.
~35% by weight, with the remainder being solid oxygen sources such as iron ore and mill scale, with a CaO/Fe ₂ O ₃ ratio of 0.6.
A lime-based smelting flux for simultaneous dephosphorization and desulfurization treatment of hot metal, characterized by a composition of ~0.9. 2 The main component is quicklime, 5 to 20% by weight of one or more solvents selected from fluorite, cryolite, and colemanite, and 10% of limestone.
~35% by weight, with the remainder being solid oxygen sources such as iron ore and mill scale, with a CaO/Fe ₂ O ₃ ratio of 0.6.
A simultaneous dephosphorization and desulfurization treatment method for hot metal, characterized by injecting a refining flux having a composition of ~0.9 into hot metal with a silicon concentration of 0.25% or less at a temperature range of 1250 to 1450°C. 3 Refining flux injection speed is 100 to 400 per minute
The method according to claim 2, wherein Kg. 4. The method according to claim 2 or 3, wherein the silicon concentration of the hot metal is 0.10% or less.