KR19990013125A - MgO-based molten iron pretreatment - Google Patents

Abstract

The present invention relates to a pretreatment for treating impurities contained in the molten iron drawn from the furnace, 30 to 45% by weight CaO, 20 to 40% by weight MgO, 10 to 15% by weight SiO ₂ , 5 to 10% by weight C , MgO-based molten iron pretreatment material comprising 1 to 5 wt% MnO, 5 to 10 wt% Al ₂ O ₃ , 1 to 5 wt% P ₂ O ₅ , 0.3 to 1.5 wt% S, and inevitable impurities The present invention relates to a technology for smoothing the composition of slag, preventing the restoration of impurities, and improving the production of products by reducing the wear rate of devices while being an inexpensive raw material.

Description

MgO-based molten iron pretreatment

The present invention relates to a pretreatment material for impurities such as sulfur, phosphorus, and silicon contained in molten iron drawn out in a road process.

Since the impurity pretreatment material causes a bad factor in the quality of the product steel depending on the impurity content in the molten iron out of the smelting furnace, after the pretreatment, LDS so that the refining operation in LDS converter (Linze Donawitze Stirring Converter) It refers to a material used to separate materials such as Na ₂ CO ₃ , CaC ₂ , CaO, etc. in molten iron before the process by vaporizing or slag-forming elements such as sulfur and phosphorus silicon.

Generally, Na ₂ CO ₃ , CaC ₂ , CaO, and CaCO ₃ systems have been used as impurity pretreatments.

Conventionally, when CaC ₂ and CaCo _3a were used as pretreatment materials, the desulfurization rate was increased when blowing CaCo ₃ ash rather than CaC ₂ , but the workability (spraying, etc.) was poor, and the formation of bond (crystal structure) at low temperature was poor. Advantageous.

When using a CaO system as an impurity pretreatment material, since the slag itself forms excessive oxidative property, impurities such as phosphorus and sulfur are restored to molten iron from the slag, and the recovery rate is increased as time passes after the pretreatment. This has risen.

However, in the case of using the MgO-based pretreatment according to the present invention, the characteristics and pretreatment of the MgO system that requires a temperature of 700 ~ 800 ℃ to decompose CaMgCO ₃ to obtain MgO at the dehydration temperature at 350 ℃ By applying the appropriate basicity method (CaO + MgO / SiO ₂ + AL ₂ O ₃ + P ₂ O ₅ ) rather than molten iron slag basicity (CaO / SiO ₂ ), the higher the MgO content, the higher the prevention of impurity recovery. The ability of the system to remain in the high temperature region up to 2800 ° C. was able to significantly suppress slag changes.

Therefore, when looking at their binding forms (Na ₂ SO ₄ , CaSO ₄ , Mg ₂ SO ₄ , Mg ₂ P ₂ O ₇ ), the anion (S, O, C, P to cations (Na, Ca, Mg ⁺⁺ )) Volatile cations of CaO and MgO, and CaSO ₄ , Mg ₂ SO ₄ and Mg ₂ P ₂ O ₇ , and CaSO ₄ causes a change in recovery reaction at low or high temperatures, but Mg ₂ SO ₄ and Mg ₂ P ₂ O ₇ maintains discomfort, that is, 350-2800 ° C.

Therefore, CaO plays an important role in molten iron, but changes with temperature, resulting in poor results.

Looking at their manufacturing process, CaC ₂

CaO + 3C = CaC ₂ + CO -114.88 kcal / mol and

At the time of sign language,

_{CaC 2 + 2H 2 O = C} 2 H 2 + Ca (OH) 2 +31.4 kcal inde contrast, MgO is produced by heating the CaMgCO ₃ 700 ~ 800 ℃.

Also, looking at the calories of hydration,

CaCO ₃ → CaO + CO ₂ -42.9 kcal / mol

CaO + H ₂ O → Ca (OH) ₂ 15.1 kcal / mol,

MgCO ₃ → MgO + CO ₂ -23.2 kcal / mol

MgO + H ₂ O-> Mg (OH) ₂ +8.11 kal / mol.

Therefore, as can be seen from the heat of dissolution and the amount of heat of hydration, MgO is more advantageous than CaO because it has a large force to decompose at low temperatures and to support high temperatures.

Table 1 shows the composition of the everber gear material which is difficult to pretreat the impurities in the molten iron during the steelmaking operation.

TABLE 1

Composition of molten iron pretreatment (% by weight)

Among iron constituents, phosphorus and sulfur may be necessary depending on the purpose of use of iron products, but in general steels, they should be pretreated because they act as impurities. Conventionally, in order to pretreat this, CaC ₂ , CaO, CaCO ₃ system was used.

Therefore, by using the pretreatment material shown in Table 1, the volatile matter which flows to the gas at the time of stirring is small, and it mostly slags and floats on the upper part of molten iron | metal. Slag floated on the upper part of molten iron should be removed. After pretreatment, the slag is prevented and removed according to the correction of basicity (CaO / SiO ₂ ) in the slag. . The slag composition according to these results is shown in Table 2.

TABLE 2

Molten iron slag composition and slag composition after pretreatment (% by weight)

As shown in Table 2, when CaC ₂ pretreatment was used, SiO ₂ , Al ₂ O ₃ wt% was low due to the decomposition composition of CaO, CaO, MnO, FeO, etc. were high, and the basicity It can be seen that the components do not change significantly. Therefore, it can be seen that it is SiO ₂ , Al ₂ O ₃ that the molten iron temperature is strongly formed at low temperatures, and that MgO, MnO, and basicity have the ability to retain the formed slag.

In addition, the CaC ₂ predictive material has a basicity of 3% by weight or less, and there is a problem in that the workability of slag composition and post-combination removal work is poor.

Accordingly, the present invention is to solve the above problems, in place of the conventional CaO pretreatment material, to facilitate the composition of the slag, to prevent the restoration of impurities, and to reduce the wear rate of the equipment while being a low-cost raw material It is an object of the present invention to provide a MgO molten iron pretreatment that improves production.

In order to achieve the above object, MgO molten iron pretreatment material according to the present invention;

30 to 45 wt% CaO, 20 to 40 wt% MgO, 10 to 15 wt% SiO ₂ , 5 to 10 wt% C, 1 to 5 wt% MnO, 5 to 10 wt% Al ₂ O ₃ , 1 to 5 wt % P ₂ O ₅ , 0.3 to 1.5% by weight S, and it is characterized by containing an inevitable impurity.

The higher the SiO ₂ component contained in the MgO molten iron pretreatment according to the present invention, the more favorable the desulfurization operation, but the content of silicon should be reduced as low as possible to improve the fluidity of the slag and lower the cohesiveness. It is preferable to make content into 10 to 15 weight%.

In addition, the CaO component preferably contains about 30 to 45% by weight in order to bond with SiO ₂ to lower the slag.

In addition, although the MgO component contained in the molten iron pretreatment material according to the present invention has a higher content, the bonding property with sulfur, phosphorus, silicon, etc. is excellent, but it is preferable to contain 20 to 40% by weight in proportion to the CaO content. Do.

On the other hand, according to the crystal bond structure of Ca, Mg, Na of the cation and S, P, O, which are anions, MgO system to be combined with Na ₂ SO ₄ , CaSO ₄ , Mg ₂ SO ₄ , Mg ₂ P ₂ SO _7, etc. The pretreatment material preferably contains 40% by weight of MgO content equivalent to CaO.

In addition, the Al ₂ O ₃ content is a bonding accelerator of MgO, CaO, SiO _2, the higher the content is to improve the fluidity of slag and to complement the coagulation force, but 5 to 10% by weight in consideration of the binding of other components Most preferred.

In addition, the carbon preferably contains 5 to 10% by weight in order to increase the carbon-potential, that is, the carburizing melting point and decrease the density to provide a carbon reducing atmosphere. 10 wt% or less is preferable because it inhibits slag composition while degrading tissue formation.

The MgO-based pretreatment material according to the present invention satisfies the condition that the condensation, trapping and decomposition of the coagulation powder is maintained at 88 µm to 1.2 to 2.3 or more, and if the low temperature decomposition is good, the humidity content must be low. In addition, in addition to these basic conditions, the addition of a coagulant combination to ensure the conditions that can be commercialized each other.

Hereinafter, the present invention will be described in detail through examples of the present invention.

230 tons / charge of molten iron from ladle from the blast furnace and equally 1500 kg / charge of CaO pretreatment material (CaC ₂ ) and MgO pretreatment, respectively, to analyze the composition of the slag produced at this time One result is shown in Table 3.

TABLE 3

As shown in Table 3, the content of SiO ₂ and Al ₂ O ₃ was increased when the CaC ₂ pretreatment was used, and the content of MgO, MnO, FeO was high when the MgO pretreatment was used, and the desulfurization reaction was increased. It can be seen that good. In addition, since the slag treated by the pretreatment material of the present invention has a viscosity, it is easy to remove impurities and the workability is good.

According to the molten iron pretreatment material according to the present invention as described above, it has the effect of smoothing the composition of the slag, to prevent the restoration of impurities, and to improve the production of the product by reducing the wear rate of the equipment while being an inexpensive raw material. .

Claims (1)

30 to 45 wt% CaO, 20 to 40 wt% MgO, 10 to 15 wt% SiO ₂ , 5 to 10 wt% C, 1 to 5 wt% MnO, 5 to 10 wt% Al ₂ O ₃ , 1 to 5 wt An MgO-based molten iron pretreatment material comprising% P ₂ O ₅ , 0.3 to 1.5% by weight S, and inevitable impurities.