RU2349646C2 - Wire for treatment of liquid cast iron in ladle - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: wire is composed of metallic sheath and sintered filler, containing mechanical mixture of magnesium powder and passivator. In the capacity of passivator it is used fused slaggy composition with content CaO≥50.0 wt %, SiO₂≤16 wt % and of basicity (CaO/SiO₂)≥3.5. Magnesium- fused slaggy composition relation is a value (0.15…1.15):1, and relation of magnesium in filler and content of filler itself in wire is in the range (0.31…1.85):1. Fused slaggy composition additionally contains CaF₂, Al₂O₃, MgO, P₂O₅, Na₂O, K₂O separately or together in any combination and relation, FeO, MnO, S. Content of (FeO+MnO) shouldn't exceed 3.0 wt %, and content of S should be ≤0.5 wt %.

EFFECT: increasing of magnesium efficiency and high-repeatablity level of desulphurising.

2 cl

Description

The invention relates to ferrous metallurgy, and in particular to out-of-furnace treatment of metallurgical melts with powdered reagents.

Known flux-cored wire for processing molten iron in a ladle, consisting of a metal shell with a thickness of less than 1 mm, filled with metallic magnesium (US Patent No. 4,205,981, published June 3, 1980). This wire cannot be effectively used for cast iron processing in the conditions of metallurgical enterprises for the following reason. Magnesium has an evaporation temperature of 1107 ° C, and the vapor pressure of magnesium at temperatures of after-furnace treatment of molten iron (1250 ... 1450 ° C) is 2.8 ... 10.6 atm. Therefore, being in the pure form in the composition of the wire, magnesium quickly and violently evaporates, leaving the melt in the form of very large vapor bubbles or even a continuous stream. All this is accompanied by a pyroelectric effect and excessive dust and gas emission above the bucket and leads to a very low degree of magnesium use for desulfurization and increased wire consumption.

The closest in technical essence and the achieved effect to the claimed one is a wire for treating molten iron with magnesium, consisting of a metal shell and a powder filler containing a mechanical mixture of 20 ... 40% magnesium powder and 80 ... 60% calcined dolomite (USSR Author's Certificate No. 1655996, published 06/15/1991, Bull. No. 22). When using it, deep passivation of magnesium occurs with an inert additive - calcined dolomite, which makes it possible to restrain the rate of magnesium evaporation and reduce the amount of magnesium vapor that enters the melt. But this wire also does not ensure the efficient use of magnesium supplied to the metal. As you know, firing dolomite is an energy-intensive process. At the same time, with an increase in the degree of firing, energy costs are progressively growing. At the same time, for the passivation of magnesium in a flux-cored wire, dolomite with a high degree of firing must be used. So, in the presence of only 0.5% calcium and magnesium carbonates in the calcined dolomite, the melt processing conditions in the ladle are substantially worsened by cored wire, dust and gas formation sharply increases. The second significant drawback of the magnesium-dolomite wire is that dolomite powder has a low fluidity, which is why it does not mix well with magnesium powder during the manufacturing process of the wire. The inhomogeneity of the mixture of powders of dolomite and magnesium both in cross-section and along the length of the wire leads to the pyroeffect and insufficient efficiency of processing the melt with magnesium. With the specified composition of the filler wire, magnesium enters the metal to be treated in the form of a continuous stream of steam, the crushing of which into individual bubbles occurs in the volume of the metal. Under these conditions, the size of the magnesium vapor bubbles that arise in the metal is determined only by the magnitude of the interfacial tension at the interface between the magnesium vapor and cast iron. The large size of the resulting bubbles leads to the fact that during the movement to the surface of the melt, the bulk of the magnesium cannot be consumed during the course of the desulfurization reaction. Unreacted magnesium vapor burns in the atmosphere above the bucket with the formation of a large number of dust and gas emissions. In addition, the calcined dolomite is not a desulfurizer and does not provide the formation of slag on the metal surface, assimilating the pop-up sulfides. All this significantly worsens the degree of magnesium use and leads to increased wire consumption.

The basis of the claimed invention is the task of improving the wire for processing molten iron in a ladle by changing the composition of the filler of the flux-cored wire in order to provide a more uniform mixture of magnesium powder with a passivator, using a desulfurizer of liquid metal as a passivator and establishing certain optimal ratios between the components of both the filler and and the whole wire as a whole. The solution to this problem makes it possible, as the wire enters the liquid melt, significantly increase the time of melting of the wire sheath, reduce the rate and intensity of magnesium evaporation, reduce the size of the magnesium vapor bubbles, and form a slag on the metal surface that assimilates the floating sulfides. This will increase the degree of use of magnesium, ensure a consistently high level of desulfurization, reduce wire consumption and significantly improve the environment during out-of-furnace cast iron processing.

The essence of the invention lies in the fact that in a wire for processing molten iron in a ladle, consisting of a metal shell and a powder filler containing a mechanical mixture of magnesium powders and a passivator, a fused slag mixture with a CaO content of> 50.0 wt.% Is used as a passivator, SiO ₂ ≤16 wt.% And basicity (CaO / SiO ₂ ) ≥3.5, and the ratio between magnesium and the melted slag mixture is (0.15 ... 1.15): 1, and the ratio between the magnesium content in the filler and the content of the filler in the wire is in lach (0.31 ... 1.85): 1. The fused slag mixture may additionally contain CaF ₂ , Al ₂ O ₃ , MgO, P ₂ O ₅ , Na ₂ O, K ₂ O individually or together, FeO, MnO, S, and the content of (FeO + MnO) should not exceed 3 , 0 wt.%, And the content of S≤0.5 wt.%.

The essential features common with the prototype are:

- metal shell;

- a powder filler that contains a mechanical mixture of magnesium powders and a passivator.

Distinctive features of the prototype essential features are:

- as a passivator use fused slag mixture with CaO content ≥50.0 wt.%, SiO ₂ ≤16 wt.% and basicity (CaO / SiO ₂ ) ≥3.5;

- the ratio between magnesium and the melted slag mixture is a value of (0.15 ... 1.15): 1;

- the ratio between the content of magnesium in the filler and the content of the filler in the wire is in the range (0.31 ... 1.85): 1.

An additional significant feature is:

- the melted slag mixture additionally contains CaF ₂ , Al ₂ O ₃ , MgO, P ₂ O ₃ , Na ₂ O, K ₂ O individually or together, FeO, MnO, S, and the content of (FeO + MnO) does not exceed 3, 0 wt.%, And the content of S≤0.5 wt.%.

The above features are necessary and sufficient for all cases to which the scope of the invention applies.

There is a causal relationship between the essential features and the technical result — increasing the degree of use of magnesium, ensuring a consistently high level of desulfurization, reducing wire consumption and significant environmental improvements during out-of-furnace cast iron processing, which is explained as follows. A characteristic feature of the ground fused slag mixture of reduced composition is its high fluidity and low hygroscopicity. So, in comparison with dolomite with the same particle size distribution, the fluidity of the ground fused slag mixture of the given composition is 1.5-2.0 times more. The high fluidity of this fused slag mixture makes it possible to obtain a homogeneous mechanical mixture of magnesium powders and fused slag mixture directly in the process of producing flux-cored wire by filling the groove-like profile of the metal strip with magnesium and the mixture that come from individual bins. The second feature of the melted slag mixture of the given composition is the absence in its composition of components that decompose at high temperature with the release of gaseous substances, which significantly reduces dust and gas emission during the processing of the melt by the inventive wire. These properties of the melted slag mixture of the reduced composition allow using it as a magnesium passivator with the solution of the technical problem posed. In addition, the fused slag mixture with CaO ≥50.0 wt.%, SiO ₂ ≤16 wt.% And basicity (CaO / SiO ₂ ) ≥3.5 is itself a desulphurizer of molten iron and will remove sulfur from the melt, increasing efficiency use of magnesium. The use of this mixture in the composition of the wire also allows during processing to form a slag on the metal surface that actively assimilates pop-up sulfides, which will ensure a consistently high level of desulfurization. The presence in the mixture CaF ₂ , Al ₂ O ₃ , MgO, P ₂ O ₅ , Na ₂ O, K ₂ O, FeO, MnO, S in the indicated amount contributes to the most efficient course of the desulfurization process. When a flux-cored wire is filled with a mechanical mixture of magnesium and a melted slag mixture of reduced composition into molten iron, the time of melting of the wire sheath is significantly increased, which allows it to sink to a greater depth and the maximum volume of metal in the ladle will be covered by the reaction of magnesium and melt. When using a wire of the given composition, the processes of magnesium release into the melt and melt of the filler are synchronized over time, preventing the formation of magnesium vapor inside the wire or releasing the filler into molten cast iron in the solid state. The use of a wire with such a filler composition allows, as it enters the molten iron, significantly reduce the rate and intensity of magnesium evaporation, and reduce the size of the magnesium vapor bubbles. In the local zone of interaction with the melt, the magnesium partially dissolves, and in part small bubbles of magnesium vapor are formed, which, rising upwards, interact with sulfur and carry magnesium sulfide into the slag created by the fused mixture. Lime (CaO) contained in the mixture in the local zone also interacts with sulfur to form calcium sulfide, which floats to the surface of the melt and is assimilated by the resulting slag. Magnesium dissolved in cast iron also reacts with sulfur, and the reaction products bubble the magnesium vapor into the slag and assimilate it. The ratio between the magnesium content in the powder filler and the filler content in the wire within the specified limits is due to the fact that if it is less than 0.31: 1, the filler will be released into the melt in the solid state and there will be additional costs for heating and melting the material, increased carbon loss magnesium. If the indicated ratio is more than 1.85: 1, this will lead to the formation of magnesium vapor inside the wire and rupture of the sheath at insufficient depth, pyroelectric effect, emissions and, as a result, reduced efficiency of magnesium use, increased wire consumption and excessive dust and gas emission. The ratio between magnesium and the melted slag mixture within the specified limits is due to the fact that if it is less than 0.15: 1, then deep passivation of magnesium will not be ensured, and the processing process will proceed with bubbling, pyroelectric effect, emissions, which will lead to a decrease in efficiency the use of magnesium and excessive dust and gas emission. If the indicated ratio is more than 1.15: 1, then there will be increased wire consumption and low economic efficiency of using magnesium.

Studies have found that if the CaO content is less than 50.0 wt.% And the basicity of the mixture is less than 3.5, then the effectiveness of additional desulfurization (due to direct interaction of CaO with sulfur) is reduced. If the content of SiO ₂ in the mixture exceeds 16.0% by weight, the desulfurizing ability of the slag mixture decreases, the assimilating ability of the coating slag decreases, and the total desulfurization efficiency decreases accordingly. When the content of (FeO + MnO) is more than 3.0 wt.%, The desulfurization indicators deteriorate due to the reaction of interaction (oxidation) of magnesium with the indicated oxides. When the content in the fused mixture S is more than 0.5 wt.%, The sulfide capacity of both the slag mixture itself and the overall slag as a whole is reduced, which will reduce the overall efficiency of the desulfurization process. Note that when using a wire of the specified composition, the main desulfurization reaction proceeds between magnesium and sulfur dissolved in the liquid metal, while the mixture acts as a passivator, improving the desulfurization indices; the presence of a specified amount of CaO in the mixture can further improve desulfurization, and the remaining components contained in the indicated amounts can stabilize desulfurization parameters at a high level. CaF ₂ , Al ₂ O ₃ , MgO, P ₂ O ₅ , Na ₂ O, K ₂ O are contained, together or separately, in the initial charge materials in the production of a fused slag mixture, while for a slag mixture based on the reduced base content of CaO and SiO ₂ , the presence of CaF ₂ , Al ₂ O ₃ , P ₂ O ₅ , Na ₂ O, K ₂ O in any possible amount will lead to an increase in the slag's fluid mobility and stabilization of its fluidity and kinetic desulfurization conditions, while maintaining the necessary level of assimilative ability of the coating slag. The presence of MgO in the slag mixture based on such a basic content of CaO and SiO ₂ , on the one hand, stabilizes the viscosity characteristics of the slag (fluidity), and on the other hand, increases the activity of CaO. Thus, for any additional content of CaF ₂ , Al ₂ O ₃ , MgO, P ₂ O ₅ , Na ₂ O, K ₂ O, indicators of total desulfurization (degree of utilization of magnesium, high level of desulfurization, together or separately with other characteristics) wire consumption) will improve and stabilize at a high level (wire consumption will decrease).

The analysis showed that the claimed invention has novelty and inventive step, and it is the specified set of essential features that provides a technical result - increasing the degree of use of magnesium, ensuring a consistently high level of desulfurization, reducing wire costs and significantly improving the environment during out-of-furnace cast iron processing.

A flux-cored wire is made as follows. The metal strip is profiled into a groove-like sheath. Dosed portions from individual hoppers fill the shell first with magnesium, and then with a passivator — a fused slag mixture with CaO = 60.0 wt.%, SiO ₂ = 15 wt.% And basicity (CaO / SiO ₂ ) ≥ 4.0, which high fluidity evenly fills the pores between the particles of magnesium. Then, with the help of roller stands, they compress the shell and form a lock. Finished wire is wound on coils and delivered to steel processing compartments.

составляет 76%. Степень десульфурации на всех обработках стабильно находилась в границах 79…83%. Процесс обработки чугуна протекал спокойно, без выбросов и барботажа. При использовании в таких же условиях проволоки, изготовленной по способу-прототипу (магния - 35 г/м, обожженного доломита - 70 г/м,), конечное содержание серы составило 0,015%, а коэффициент использования магния на десульфурацию - 45,6%, причем процесс обработки сопровождался пироэффектом и чрезмерным пылегазовыделением. Степень десульфурации была низкой и нестабильной и находилась в пределах 35…58%. Для получения равнозначного конечного содержания серы расход магния составит 0,42 кг/т или будет на 68% большим.At one of the metallurgical plants tested the proposed wire. The cast iron desulfurization unit / UDM / is supplied with molten cast iron in 100-ton cast-iron ladles, which are installed in the production places for processing. Flux cored wire filled with a mixture of magnesium and fused slag mixture of reduced composition (magnesium - 35 g / m, mixture - 70 g / m, magnesium content in the filler - 33%, filler content in the wire - 41%, the ratio between magnesium and fused slag mixture - 0.5: 1, the ratio between the content of magnesium in the filler and the content of the filler itself 0.80: 1) is introduced using a tribameter into molten iron at a speed of 2.0 m / s. Conducted 10 treatments. The initial sulfur content in cast iron (S _n ) averaged 0.030%, the final (S _k ) - 0.005%, the consumption of magnesium (q _Mg ) was 0.25 kg / t. The utilization of magnesium for desulfurization

is 76%. The degree of desulfurization in all treatments was stably in the range 79 ... 83%. The processing of cast iron proceeded calmly, without emissions and sparging. When using under the same conditions a wire made by the prototype method (magnesium - 35 g / m, calcined dolomite - 70 g / m), the final sulfur content was 0.015%, and the utilization of magnesium for desulfurization was 45.6%, moreover, the processing process was accompanied by a pyroelectric effect and excessive dust and gas emission. The degree of desulfurization was low and unstable and ranged from 35 ... 58%. To obtain an equivalent final sulfur content, the magnesium consumption will be 0.42 kg / t or will be 68% higher.

Claims (2)

1. A wire for processing molten iron in a ladle, consisting of a metal sheath and a powder filler containing a mechanical mixture of magnesium powders and a passivator, characterized in that a fused slag mixture with a CaO content of 50.0 wt.%, SiO _{2 is} used as a passivator ≤16 wt.% And basicity (CaO / SiO ₂ ) ≥3.5, and the ratio between magnesium and the melted slag mixture is (0.15 ... 1.15): 1, and the ratio of the content of magnesium in the filler to the content of the filler itself in the wire is in the range (0.31 ... 1.85): 1. 2. The wire according to claim 1, characterized in that the fused slag mixture further comprises CaF ₂ , Al ₂ O ₃ , MgO, P ₂ O ₅ , Na ₂ O, K ₂ O individually or together, FeO, MnO, S, moreover, the content of (FeO + MnO) does not exceed 3.0 wt.%, and the content of S≤0.5 wt.%.