KR20030023908A - A Method for Refining Hot Metal in a Converter with High Efficiency of Dephosphurization - Google Patents

Abstract

PURPOSE: A method for refining hot metal in converter with high dephosphorization efficiency is provided, which is characterized in that low basicity slag generated in refinement of tire cord steel is used as a supplementary raw material to remove phosphorus in hot metal, thereby reducing the amount of expensive supplementary raw materials such as fluorite and quicklime. CONSTITUTION: The method is characterized in that a low basicity slag comprising CaO 45.3 to 55.0 wt.%, SiO2 44.9 to 50.4 wt.%, Fe 0.7 to 1.5 wt.%, MgO 5.0 to 7.0 wt.%, MnO 1.0 to 1.5 wt.%, Al2O3 0.6 to 1.1 wt.%, P2O5 0.02 to 0.04 wt.%, S 0.01 to 0.02 wt.%, TiO2 0.02 wt.% or less is poured into converter in an amount of 3 to 5 kg per total charged iron (hot metal+scrap) during converter blowing; and the low basicity slag is again poured into converter in an amount of 3 to 5 kg per total charged iron (hot metal+scrap) at a point of time when the converter blowing operation is progressed by 65 to 75 %.

Description

A method for refining hot metal in a converter with high efficiency of dephosphurization

The present invention relates to a method for refining a converter of a low-lining steel, and more particularly, by using slag of a low-basicity by-product as a by-product as a by-product as a secondary material for the removal of phosphorus while promoting the slag regeneration rate, a converter that effectively reduces phosphorus and reduces the amount of auxiliary material used. It relates to a refining method.

Generally, the steelmaking process consists of charter preliminary treatment → converter refining → secondary refining → continuous casting process. In this series of steelmaking processes, converter refining is made by charging hot iron and scrap as raw materials into the converter and casting the molten iron.Simultaneous raw lime, calcined dolomite (CaO, MgO), Sintered ore, fluorspar, etc. are added to collectively perform a series of operations to remove impurities such as carbon, silicon, manganese, phosphorus, sulfur, titanium, etc. from molten iron by oxidative refining. During the melting of molten iron, the decarburization operation as in Scheme 1 is the main reaction.

[C] + 1 / 2O ₂ = CO (g)

[C] + O ₂ = CO ₂ (g)

According to the removal rate of carbon proceeded by the decarburization reaction, that is, the converter refining operation may be divided into the initial stage, the middle stage, and the last stage. Specifically, in the early stage of blowing, the blowing proceeds as [Si] in the molten iron is oxidized and removed, and the decarburization reaction proceeds simultaneously. In the middle of blowing, decarburization occurs most actively. [Si] is completely removed from molten iron, and almost all of the oxygen blown through the lance reacts with carbon in the molten iron to generate CO gas. The denitrification reaction as in Scheme 2 proceeds.

[N] = 1 / 2N ₂

Silicon in molten iron is known to be the first element that reacts with oxygen when the converter is blown, and the oxidation reaction of silicon and oxygen plays an important role as a heat source necessary to raise the temperature of molten iron during the blow. Oxide produced by the reaction of silicon in the molten iron with oxygen (SiO ₂ ) is unstable at the steelmaking temperature, it is necessary to combine the basic oxide in the slag to form a stable complex oxide form. As a basic oxide, quicklime is typically present in the form of (2CaO) (SiO2) (Di-calcium-silicate) by combining with SiO ₂ generated during blowing, and the basic oxidation equation for the production process is as follows.

[Si] + O ₂ = (SiO ₂ )

On the other hand, the dephosphorization reaction in the converter refining industry is characterized in that the so-called preferential dephosphorization occurs in which dephosphorization proceeds before carbon is lowered by the goods during the injection of quicklime. In general, the representative dephosphorization equilibrium reaction between slag and molten iron is as follows.

2 [P] + 5 [O] + 4CaO = 4CaO, (P ₂ O ₅ )

As can be seen in Scheme 4, the conditions required for dephosphorization are advantageous as the slag basicity is higher and the potential of oxygen is higher, and the lower the temperature is, the better. The removed phosphorus is present in the slag layer as it is slag and is a method of converter work.

Korean Patent Laid-Open Publication No. 2000-42501 is a conventional technique for effectively inducing the Tallinn reaction to manufacture low-lining steel. In this technology, 0.8 ~ 2.0% by weight of light dolomite is added to the converter leaving 15-40% of the slag of the previous operation, and the furnace is tilted to coat the slag on the furnace wall, followed by 1.5 ~ 2 weight of lime for protection of the furnace body. After adding%, load the scrap metal, and then the molten iron, and then the molten iron in the furnace is commenced by Songsan. At the same time, 0.5-1.5% by weight of quicklime and 0.3-1.5% by weight of sintered ore are added. At 30 ~ 70% of the blowing time, 0.1 ~ 0.3% by weight of one or more selected from quicklime, light small dolomite, and sintered ore was added to the total charge, and the chemically labile phosphorus compound in the high carbon region was stably maintained in the slag, 0.2 wt.%. Refining method for the production of molten steel containing less than% phosphorus and sulfur. In this technology, by-products such as quicklime are added to produce low-lining steel, and they do not use by-products.

The present invention provides a converter refining method for stably manufacturing low-lining steel by reducing the input amount of by-products by inputting slag as a byproduct into the converter, and easily controlling the content of phosphorus and sulfur at the end point to the same or lower level. Its purpose is to.

1 is a graph showing the change in basicity according to the blowing time

In the converter operation method of the present invention for achieving the above object, the low-basic degree ladle slag containing CaO: 45.3-55.0% by weight, SiO ₂ : 44.9-50.4% by weight at the time of 5-15% conversion of the converter molten steel Including 3 to 5kg per ton, and at the 65-75% time point of the progress of the charging, the low base also comprises slag in the range of 3 to 5kg per ton of charged molten steel.

Hereinafter, the present invention will be described in detail.

The present inventors have concluded that lowering the basicity and increasing the amount of CaO, which has a beneficial effect on phosphorus control, in order to increase the slag recyclability in the research process for manufacturing low-lining steel, is advantageous for the production of low-lining steel. While searching for the solution, the low base material generated as a by-product when refining molten steel for tire cords was noticed. This low base slag contains 45.3-55.0 wt% of CaO and 44.9-50.4 wt% of SiO ₂ , which is low in basicity and fairly high in CaO. Table 1 below shows the components of the low base slag and other slags.

Slag composition Converter slag (% by weight) General Ladle Slag (wt%) Low Base Slag (% by weight) Fe 12.5-27.0 0.1-4.0 0.7-1.5 CaO 34.5 ~ 41.2 25.0-45.9 45.3-55.0 SiO ₂ 11.5-15.5 24.9-42.4 44.9-50.4 MgO 7.0-11.5 8.0-12.0 5.0 ~ 7.0 MnO 3.8 ~ 4.2 1.0-1.5 1.0-1.5 Al ₂ O ₃ 2.0 ~ 3.0 2.6 ~ 4.1 0.6 to 1.1 P ₂ O ₅ 1.8 ~ 2.2 1.5 ~ 3.0 0.02-0.04 S 0.3 ~ 0.5 0.02-0.05 0.01 ~ 0.02 TiO ₂ 0.07-0.19 0.07-0.12 0.02 or less Configuration Converter Slag Converter Slag + Alloy Oxide Converter Slag + Alloy Iron Oxide + Quicklime A flux + quicklime

As can be seen from Table 1, low-basicity slag has a high basic content of SiO _2, which determines slag recyclability compared to converter refining slag, and has a low basicity and a large amount of CaO necessary for phosphorus control. In addition, the contents of phosphorus (here, oxide form P ₂ O ₅ ) and sulfur, which are harmful elements in molten steel, are low. Low-basicity slag generated as a by-product when refining the molten steel for tire cords in Table 1 is made by tapping the molten steel for tire cords after refining the converter and after newly exhausting the slag. It is created by flux.

Input (kg) A-Flux ingredient list (% by weight) quicklime 4kg / t-s CaO SiO ₂ Al ₂ O ₃ A-flux 7kg / t-s ≥44 53-55 3% <

In the present invention, the low base degree slag (CaO: 45.3-55.0 wt%, SiO ₂ : 44.9-50.4 wt%) generated as a by-product when refining the molten steel for tire cords is introduced into the converter refining process. It is characterized by the fact that it is promoted to produce low-lining steel. Therefore, in the present invention, any molten iron produced from the blast furnace can be applied to any converter, for example, by weight%, [C]: 4.0 to 4.6%, [Si]: 0.2 to 0.5%, [P] For example, molten iron including 0.7 to 1.0% and nitrogen concentration of 50 to 70 ppm.

In the present invention, the low-basicity slag is introduced into the converter refining operation. At this time, the conversion of the converter blow pattern and other auxiliary materials is performed according to a conventional method. In other words, the main raw materials are molten iron and scrap metal into the converter, and at the same time, the subsidiary materials are added to the Songsan and refining the converter. In this process, the input amount of the subsidiary materials input after the middle stage is adjusted in consideration of the slag content and the phosphorus content after the middle stage of the blow.

First, ladle slag of low base air is injected at the beginning of the converter blow process. In the early stage of blowing, high slag of quick-melting lime or light dolomite is added, so slag is difficult to produce, which makes it difficult to effectively remove tallin. Therefore, when the slag of the present invention is added to the slag, it is easily and uniformly dispersed into the slag, so as to secure CaO, (P ₂ O ₅ ), which is refined as in Scheme 8, to promote the slag goods, thereby effectively phosphorus in molten iron. It is easily transferred to the slag layer, which is very advantageous for the Tallinn reaction. Introducing low-basic slag at the initial stage of blowing is preferably 5-15% at the time of blowing, since it is the most desirable time to induce effective Tallinn behavior.

2 [P] + 5 [O] + 4 [CaO] = 4CaO, (P ₂ O ₅ )

The amount of ladle slag injected at 5 to 15% of the blowing rate is preferably in the range of 3 to 5 kg per tonne of charged molten steel. In case of low slag loading at the initial stage of slag less than 3kg / t-s, it is difficult to lower the slag low temperature and promote the goods of pre-injected subsidiary materials, so it is difficult to remove phosphorus in molten iron effectively. On the contrary, if it exceeds 5kg / t-s per ton, slag goods may be generated quickly in low base condition, which may cause initial sloughing.

Next, ladle slag with low baseline is injected at 65 ~ 75% of the drilling progress. This is to induce efficient delineation reaction by promoting the quicklime of quicklime and light dolomite, which are divided into 15 ~ 80% of the time of blowing. In other words, the slag composition is very important because the oxidation reaction in the converter at the 60-70% of the blows leads to the decarburization reaction, and thus the manganese ridge phenomenon occurs in which the oxidized manganese is reduced in the early stage of the blow. At this time, the low base is also to prevent the reduction of (P ₂ O ₅ ) in the slag since the slag is re-injected to promote the re-ization of unreacted quicklime.

At this time, the added slag is preferably added in the range of about 3 to 5kg with respect to the total amount charged. If slag is put in less than 3kg per ton during the drilling, the slag will not be ignited, and as a result, the delinquency effect of molten iron is insufficient due to insufficient induction of de-manganese as well as Tallinn. In addition, when the slag is added in excess of 5kg per ton of molten steel, the viscosity of the slag in the furnace which is advantageous for the delineation reaction due to the low melting point of the slag layer drops suddenly, and the emission of the generated gas may be delayed, thereby causing the slope.

Hereinafter, the present invention will be described in more detail with reference to Examples.

EXAMPLE

The low base degree slag of Table 1 was put into a converter as Table 3, and converter operation was performed. The use of the blowing pattern and the subsidiary materials was carried out in the usual way, and the low base also added slag.

division Primary input 2nd input In-house reaction state End point content (%) Input time input Input time input Comparative Example 1 Before blow 10 none - Blowing 10% point of time 18 Comparative Example 2 Before blow 10 50 10 × 20 Comparative Example 3 Before blow 5 none - ◎ 18 Comparative Example 4 Before blow 5 50 5 ○ 18 Comparative Example 5 10 10 70 10 × 17 Comparative Example 6 10 7 70 7 △ 19 Comparative Example 7 20 10 80 10 × 20 Comparative Example 8 20 5 80 5 ◎ 17 Comparative Example 9 30 10 70 10 × 16 Comparative Example 10 30 5 70 5 ◎ 16 Inventive Example 1 5 5 65 5 ◎ 13 Inventive Example 2 5 3 65 3 ◎ 14 Inventive Example 3 10 5 70 5 ◎ 12 Inventive Example 4 10 3 70 3 ◎ 12 Inventive Example 5 15 5 75 5 ◎ 13 Inventive Example 6 15 3 75 3 ◎ 15 Inventive Example 7 5 5 75 3 ◎ 14 Inventive Example 8 5 5 75 3 ◎ 13 Inventive Example 9 10 3 65 5 ◎ 14 Inventive Example 10 10 5 65 3 ◎ 14 (Double-circle): Good ○: Slope sludge generate | occurence (triangle | delta): Slope generate | occur | produced x: Slope sludge large occurrence

As shown in Table 3, it can be seen that when the input time and the input amount of the present invention are satisfied, the internal reaction state is also good and the end point content can be lowered.

Example 2

Leave 8-12 tons of total slag lastly operated in a 100-ton converter, add 1.5 tons of light dolomite to protect the walls, and apply slag to the furnace walls 1 to 3 times to protect the impact of the charging side walls. In order to charge 1.5 tons of quicklime, 10 wt% of the total amount of scrap iron and more than 90 wt% of molten iron having the components shown in Table 4 was charged to the converter.

Chemical composition (% by weight) C Si Mn P S Ti Fe 4.4-4.6% 0.2-0.5% 0.2-0.5% 0.07-0.11% 0.003-0.023% 0.035-0.070% Remainder

After stirring the furnace body twice, refining was carried out by adding a blowing pattern and a subsidiary material in a normal manner. Table 5 shows the chemical compositions of various subsidiary materials and cooling materials used in the refining operation.

division Chemical composition (% by weight) CaO MgO T.Fe MnO SiO ₂ Al ₂ O ₃ TiO ₂ CaF ₂ C quicklime 92.5 2.20 0.39 - 0.92 0.30 - - - Dolomite 56.16 38.80 0.60 - 1.40 0.51 - - - fluorite - - - - 13.54 - - 83.86 - Sintered ore 8.42 1.24 48.29 0.42 4.54 1.56 0.17 - 2.60

In case of blowing pattern and subsidiary materials, as in the case of injecting raw materials, 500 ~ 1000kg of quicklime and 300 ~ 1000kg of sintered ore are added according to the silicon content in molten iron (when the heat source is secured according to the heat blending calculation), and the blowing time is 5 ~ At 80%, the low-basicity slag and light dolomite of Table 1 were divided into 200 to 250 kg two to four times each. In addition, about 80-85% of the blowing time, about 300-800 kg of sintered ore was introduced.

In the converter refining of molten iron with a silicon concentration of 0.25% or less in molten iron, such as de-silicon and dephosphorized molten iron, SiO ₂ is too low in slag, and the slag fluidity is lowered during the drilling. Fe-Si (ferrosilicon) of Fe-Si (ferrous silicon) in the furnace by adding 0.1 ~ 0.3kg (wt%) to secure the slag fluidity, the burden of additional cost to make the quicklime is easily generated.

However, in the present invention, SiO ₂ is 34.9 to 42.4 (wt%) of slag injected during the blowing process to ensure the ashability of slag without introducing ferrosilicon even when remelting molten iron in the molten metal of 0.25% or less. It became. However, low-basicity does not add more than 0.5% of the silicon content in the molten iron in the slag because the slag's recyclability may be too high when the slag is injected in a large amount of slag. The feeding time was divided into 5 ~ 15%, 5 ~ 75% divided into 300 ~ 500kg twice.

Except that slag was divided into 3.0 ~ 5.0kg / ts of slag based on the total loading amount during the drilling, the refining was performed in the same way as the conventional converter refining method, and the molten steel component was collected and analyzed as follows. The composition was shown.

Molten steel component and composition (% by weight) at the end point Conventional method The present invention [C] [P] [S] [C] [P] [S] 0.04 0.014 0.015 0.04 0.013 0.014 0.05 0.015 0.012 0.05 0.012 0.012 0.06 0.018 0.015 0.06 0.015 0.013 0.07 0.016 0.014 0.07 0.017 0.014 0.08 0.017 0.013 0.08 0.016 0.012 0.09 0.019 0.014 0.09 0.017 0.013 1.0 0.018 0.013 1.0 0.017 0.013

Slag composition Conventional method The present invention Fe 12.5-27.0 12.0 ~ 25.0 CaO 36.5 ~ 42.2 39.2-45.2 SiO2 11.5-15.5 11.8-16.5 MgO 7.0-15.5 7.0-11.3 MnO 3.8 ~ 4.2 3.8 ~ 4.2 Al2O3 2.0 ~ 3.0 2.0 ~ 3.0 P2O5 1.8 ~ 2.2 1.6-2.0 S 0.3 ~ 0.5 0.2-0.4 TiO2 0.07-0.19 0.07-0.18

The components of slag and molten steel are superior to the conventional converter refining method, and the recyclability rate of quicklime is also excellent according to the blowing time, showing good basicity. According to the present invention, it is possible to stably refine a steel having a phosphorus and sulfur content of about 0.02% by weight or less, regardless of carbon concentration.

As described above, according to the present invention, by recycling the slag of low-basicity generated in the refining process of the steel for tire cords, the content of phosphorus and sulfur is less than 0.02% by weight and 0.04 to 0.10% by weight of carbon at the end of the converter refining operation. Can be controlled, and excellent in initial slag goods of molten iron which is 0.25 wt% or less by the contribution of useful SiO ₂ among slag, and it is very effective in cost and waste management by reducing 50 ~ 100kg of fluorspar use, which is a solvent It can be seen that there is a useful effect.

Claims (2)

In the converter operation method, At the time of 5-15% of conversion, low-basicity slag containing CaO: 45.3-55.0% by weight and SiO ₂ : 44.9-50.4% by weight is added in the range of 3-5Kg per ton of steel for charging, and again 65 ~ The method for refining converter with excellent delineation efficiency, characterized in that the low-basicity slag at a 75% time point is included in the range of 3 ~ 5Kg per ton of steel for full charge. The method of claim 1, wherein the low-basicity slag is a by-product generated during the refining process of the tire cord steel, CaO: 45.3 ~ 55.0 wt%, SiO ₂ : 44.9 ~ 50.4 wt%, Fe: 0.7 ~ 1.5 wt%, MgO : 5.0 to 7.0% by weight, MnO: 1.0 to 1.5% by weight, Al ₂ O ₃ : 0.6 to 1.1% by weight, P ₂ O ₅ : 0.02 to 0.04% by weight, S: 0.01 to 0.02% by weight, TiO ₂ : 0.02% by weight The converter refining method having excellent delineation efficiency, characterized in that the composition is less than%.