KR930006640B1 - Dephosporus agent for preheat treatmenting of molten metal - Google Patents

Abstract

A dephorsphorising agent for molten pig iron includes 60-80 wt.% sencondary dust of converter furnace, 10-38 wt.% dust of electric furnace and additive containing 5-10 wt.% lime (CaO) and 1- 3 wt.% fluorite (CaF2). The converter furnace dust contains 85- 95 wt.% Fe, 2-12 wt.% CaO, 0.2-2.0 wt.% SiO2, 0.8-15 wt.% MgO, 1-2 wt.% MnO and 0.1-0.5 wt.% carbon and its size distribution is 85-90 % for 40-250 meshes. The electric furnace dust contains 13-15 wt.% Fe, 75-85 wt.% CaO, 4-6 wt.% SiO2, 1-3 wt.% MgO and less than 1-3 wt.% Cr and/or C and its size distribution is 80-85 % for 40-250 meshes.

Description

Dephosphorizer for molten iron pretreatment

The present invention is a molten iron used to remove the phosphorus (P) in the molten iron in the Torpedo, charging ladle (Charging Ladle or Open Ladle) that is a step before charging the molten iron from the blast furnace into the steelmaking converter It relates to dephosphorization.

In general, cold rolled products that require high processability such as automotive exterior materials require phosphorus content of 0.008% or less, but the refining process and the load of the oxygen phase, low odor combined blown converters only require refining limits and functional load. Preliminary dephosphorization has been carried out in the charter party.

Conventional dephosphorization agents used in molten iron dephosphorization include mill scale 55%, quicklime (CaO) 35%, fluorite (CaF ₂ ) 5%, and soda ash (Na ₂ CO ₃ ) 5%. In this case, the dephosphorization rate is less than 60%, and mill scale needs to be pulverized into fine particles. Soda ash is expensive, so the price is higher than the discount efficiency. The splash of the molten iron due to the intense reaction of the meeting is severe, causing workability to be deteriorated.

In addition, Korean Patent Publication No. 89-19 proposes a molten iron dephosphorizing agent containing 15-20% of fluorspar and 4-10% of soda ash. However, the dephosphorization agent is excellent in dephosphorization efficiency, but the refractory erosion of the slag area is so severe that it increases the refractory use cost and maintenance cost, and can be applied only in Torpedo Ladle Car due to the high molten iron scattering in the charging ladle. There is a disadvantage.

Also, as in Japanese Patent Publication Nos. 59-10974 and 61-881, molten iron dephosphorizers with up to 40% of fluorite and up to 50% of soda ash are proposed, but such dephosphorizers are expensive. Of course, refractory use costs and maintenance costs rise, soda ash recovery equipment and processes are required, and the molten iron fugitive due to the intense reaction of soda ash can not be used in the charging ladle.

As described above, the molten iron dephosphorizer developed so far has the following common problems.

First, the price is high, and second, the unit price and maintenance cost of refractory erosion are increased. Third, soda ash recovery equipment and process are needed. It is not applicable to ladles and can only be processed in topedores and has the problem of causing environmental pollution due to dust and flames.

Therefore, the present invention is to increase the added value of the by-products of the steel mill as a main composition as a dephosphor for the molten iron pretreatment, as well as the disadvantages of the conventional dephosphor, the high price of the refractories, the increase in the cost of use of refractory, soda meeting It is proposed to solve the additional requirements of recovery facilities and processes, and the impairment of workability due to the severe molten iron fugitive reaction by soda ash reaction and the impossibility of dephosphorization treatment in the charging raid. By recycling the dust collection dust generated by the work with the molten iron degreasing agent, it is possible to prevent the environmental pollution caused by the scattering of the molten iron during pretreatment of the molten iron, to provide high value-added iron by-products of ironworks, and to provide a low cost molten iron for the treatment of molten iron. It is.

In order to achieve the above object, the dephosphorant for pretreatment of the molten iron of the present invention by weight%, converter secondary dust; 60-80%, electric furnace; 10-38%, quicklime (CaO); 5-10% and fluorspar (CaF ₂ ); Characterized by the composition is composed of 1-3%.

The converter secondary dust and electric furnace of the present invention are by-products generated from the actual operation of steel mills. The particle fraction of 40-250 mesh accounts for 80% or more, and thus the dephosphorization reaction rate is high. It is very fast to increase the dephosphorization efficiency. Especially, CaO in the electric furnace and the converter secondary dust is combined with iron oxide and mixed with iron oxide. Done.

In addition, the chemical composition of the converter secondary dust is T.Fe; 85-95%, CaO: 6-12%; SiO ₂ ; 0.5-2.0%, MgO; 0.8-1.5%, MnO; 1-2%, C; It is composed of 0.1-0.5% of composition, the T, Fe mainly serves as a solid oxygen source as FeO, Fe ₂ O ₃ .

In addition, the electric furnace is T, Fe; 13-15%, CaO: 75-85%; SiO ₂ ; 4-6%, MgO; 1-3%, C and Cr; It has a composition of 1% or less, and the T and Fe are mostly FeO, and the CaO has an average of 13 (CaO / SiO ₂ ) of its own, which increases the dephosphorization efficiency and the form of the phosphate after dephosphorization is 3 CaO.P _2. It becomes O ₅ or 4 CaO.P ₂ O ₅ and contributes greatly to preventing the _double copying phenomenon.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

When the secondary dust of the converter is less than 60%, compared to the phosphorus content in the molten iron, not only is there a lack of a solid oxygen source but also the dephosphorization reaction rate is lowered even if the blowing amount is increased, so that the dephosphorization rate after Chiri is not more than 70%, and more than 80% The decay rate and dephosphorization rate are lowered as the CaO content decreases and the basicity is lowered, and the amount of re-coating after dephosphorization is over 0.005%. Therefore, it is preferable to make the content of converter secondary dust 60-80%.

Since the ionizing rod contains CaO as the main component, the basicity decreases at 10% or less, so that the dephosphorization condition is not satisfied. Therefore, the dephosphorization rate is not more than 70%, and at 38% or more, the basicity is increased so that the dephosphorization condition is satisfied. However, due to the relatively reduced solid oxygen supply for the first dephosphorization reaction, 2 [P] +5 [O] = (P ₂ O ₅ ) becomes inactive and moves to slag (P ₂ 0 ₅ ) Since the formation of stable phosphide decreases, the problem of increasing the double salvage also occurs, so the content is preferably 10-38%.

The reason for adding 5-10% of the quicklime (CaO) is to mutually adjust the addition ratio of the ionizing dust and the mixing ratio of the converter secondary dust, and when adding up to 38% of the electric dust is sufficient without adding the quicklime The dephosphorization rate can be secured, but in the case of increasing the amount of secondary dust in the converter by lowering the mixing ratio to 24% and 10%, the slag basicity is increased by adding 5% at 24% electric dust and 10% at 10% electric dust. By maintaining the increase in the dephosphorization efficiency it is possible to secure a dephosphorization rate of 82-87%.

When the content of fluorite (CaF ₂ ) is less than 1%, the flowability of slag is lowered so that the dephosphorization rate is lowered, and when the content is more than 3%, fluidity is good, but the content is 1-3% because the refractory is eroded. It is preferable.

The present invention consisting of the above composition of the present invention, while reducing the quicklime content of 5-10%, the forming content of 1-3% used as the cast product of the conventional dephosphor, while the by-product of the steel mill secondary dust and electric furnace dust By increasing the content, phosphorus in the molten iron is removed by the following reaction.

In general, the dephosphorization reaction in the molten iron can be represented by the following formula (1),

(P ₂ O ₅ ) generated in the formula (1) is moved to the slag and (P ₂ O ₅ ) is bonded to CaO 3 CaO.P ₂ O _{5 which} is a stable phosphide form.

Therefore, the dephosphorization reaction as shown in Equation (1) also easily occurs a double reaction (reverse reaction), so that (P ₂ O ₅ ) moved to slag is 3 CaO.P ₂ O ₅ or 4 CaO.P ₂ O, which is a stable phosphide form. this is a means of improving the reaction efficiency dephosphorization of the molten iron and prevent bokin phenomenon that takes place such that the ₅ reaction is as follows.

Therefore, as can be seen in the above (2), (4), (6), it can be seen that the reaction of (3), (5) can proceed more easily than the (1) reaction, This prevents not only the shape of the efficiency of the dephosphorization reaction of the molten iron but also the compounding phenomenon.

On the other hand, soda ash (Na ₂ CO ₃ ) commonly used during molten metal dephosphorization can be dephosphorized without oxidizing agent because FeO is formed during decomposition, but CO gas is released by the reaction as shown in the following formula (7). Reaction vessels such as these, there is a problem that the demolition work is poor enough due to the scattering of the molten iron.

However, the dephosphorization agent of the present invention does not add the expensive soda ash at all, and by adding only a small amount of fluorspar and quicklime as main raw materials of converter secondary dust and electric furnace, which are by-products of steel mills, to improve dephosphorization efficiency and prevention of poorness, It is effective in reducing the cost of refractory use and repair cost, and preventing environmental pollution and improving workability.

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

EXAMPLE

Dissolve the blast furnace in 100kg high frequency induction furnace to remove silicon, remove the slag, and add phosphorus to adjust the molten iron content to 0.097% as in actual operation, and keep the temperature at 1350 ± 5 ℃ (Powder injecter) by blowing each of the dephosphorizing agent as shown in Table 1, the non-linear state of the molten iron was visually observed.

TABLE 1

The chemical composition of the converter secondary dust and the electric dust of the present invention of Table 1 were as shown in Table 2 below, 5 minutes, 30 minutes after the removal of the dephosphor injecting the dephosphorization in order to evaluate the dephosphorization effect into a 6φ quartz tube The molten iron was collected and analyzed and the results are shown in Table 3 below.

TABLE 2

TABLE 3

As shown in Table 3, the phosphorus content of the molten iron before dephosphorization was 0.097-0.100%, and the phosphorus content after the treatment showed a high dephosphorization rate of 82-87% as 0.013-0.017% in the present invention. The dephosphorization rate of 57% was shown as 0.042.

In addition, after 30 minutes of dephosphorization, the phosphorus content returned to the molten iron was only 0.002-0.003% in the present invention, but in the comparative material, the phosphorus content in the final molten iron was reduced after the actual treatment because 0.009% was doubled. Much higher than the amount.

The molten iron fugitive state at the time of blowing in the dephosphorizing agent had no soda ash at all in the present invention, and the powder particles were fine and there was no pulsation shape, so there was almost no scattering state. As the size was more than 40 mesh, the pulsation phenomenon occurred during the blowing, and the molten iron was more severe and dust was generated by the flame.

Therefore, the workability and environmental pollution state in the dephosphorization treatment of the molten iron is very good in the present invention, but in the case of the comparative material is very poor workability in the Torpedo Ladle (Torpedo Ladle) there is no big problem in the dephosphorization workability, but recently It can be seen that the dephosphorization treatment in the applied open ladle may cause a big problem in the dephosphorization work.

As described above, according to the present invention, since the dephosphorizing agent formed by adding only a small amount of fluorspar and quicklime as main raw materials of the converter secondary dust and the electric furnace dust, which are by-products of the steelworks, has the following effects.

end. Since there is no molten metal bar phenomenon in the charter work, the workability is improved, and in particular, the charter work in the charging ladle becomes possible.

I. Since the amount of fluorspar is reduced and soda ash is not added at all, there is almost no refractory erosion and thus the unit cost of refractory can be greatly reduced.

All. Since dephosphor castability is converter secondary dust and electric furnace dust, stable supply and price of raw materials are extremely low.

la. The dephosphorization efficiency is high, and in particular, since the amount of abdomen after dephosphorization treatment is small, it is advantageous also in manufacture of extremely low toughness steel.

Claims (3)

In weight percent T.Fe; 85-95%, CaO: 2-12%, SiO ₂ ; 0.2-2.0%, MgO; 0.8-1.5%, MnO; 1-2%, C; Converter secondary dust 60-80% containing 0.1-0.5%; With T.Fe 13-15%, CaO: 75-85%, SiO ₂ ; 4-6%, MgO; 1-3%, C and Cr; 10-38% of electric furnace dust containing 1% or less as a main component, and as an additive component, quicklime (CaO); 5-10% and fluorspar (CaF ₂ ); Dephosphor for the molten iron pre-treatment, characterized in that the addition of 1-3%. The dephosphorant for preliminary treatment of molten iron according to claim 1, wherein the particle distribution of the converter secondary dust is 85-95% of 40-250 mesh. The dephosphorant for pretreatment of the molten iron according to claim 1, wherein the particle distribution of the electric dust is 40-250 mesh is 80-85%.