RU2299248C2 - Wire for out-of-furnace treatment of metallurgical melts - Google Patents

Abstract

FIELD: metallurgy, namely out-of-furnace treatment of cast iron by means of powdered reagents.

SUBSTANCE: wire includes metallic envelope and powder filler containing magnesium, silicon and iron. Magnesium is added to composition of filler after mixing magnesium with silicon and iron alloy at relation (0.1 - 1.2) : 1. Magnesium content in wire consists of 8 - 29 mass %. Invention provides increased time period of melting wire envelope, lowered speed and intensity of magnesium evaporation, lowered size of magnesium vapor bubbles.

EFFECT: increased degree of magnesium usage, stable level of high degree of desulfurization and modification, enhanced ecology at out-of-furnace treatment of cast iron.

Description

The invention relates to the industry of ferrous metallurgy, and in particular to out-of-furnace treatment of cast iron with powdery reagents.

Known flux-cored wire for out-of-furnace treatment of cast iron, consisting of a metal shell with a thickness of less than 1 mm, filled with metallic magnesium [1]. This wire cannot be used effectively for cast iron processing in the conditions of metallurgical enterprises for the following reasons. 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 costs.

Also known is a wire for adding magnesium to iron-based melts, consisting of a metal sheath and a powder filler containing a mechanical mixture of 20 ... 40% magnesium powder and 80 ... 60% calcined dolomite [2]. When it is used, 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 entering the melt. But this wire also does not provide effective use of magnesium entering the metal. 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 formed in the metal is determined only by the magnitude of the interfacial surface at the interface between the magnesium vapor and molten iron. The large size of the resulting bubbles leads to the fact that during movement to the surface of the melt, the bulk of the magnesium cannot be effectively used for desulfurization and modification. Unreacted magnesium vapor burns in the atmosphere above the bucket, which is accompanied by the formation of a large number of dust and gas emissions. All this significantly affects the degree of use of magnesium and also leads to increased consumption of wire.

The closest in technical essence and the achieved effect to the claimed is a wire for out-of-furnace treatment of metallurgical melts, consisting of a metal shell and a powder filler containing magnesium in the form of an alloy with silicon in a ratio of 1: (1.5 ... 3.0) and iron [3]. The introduction of magnesium into molten iron in an alloy with silicon and iron can significantly reduce the elasticity of dissociation of magnesium vapor, and they manage to react with sulfur in the depth of the melt. This achieves an almost complete deep passivation of magnesium and the processing of cast iron proceeds quietly, without sparging and emissions, which can significantly reduce dust and gas emission and significantly increase the degree of use of magnesium. But this method also has several disadvantages. The use of magnesium in the filler wire in the form of a finished alloy with silicon and iron does not allow to synchronize the time of release of magnesium into the melt with the time of melting of the alloy, which can lead to the formation of magnesium vapor inside the wire and rupture of the shell of the wire at an insufficient depth and, as a result, decrease in efficiency use of magnesium. The relationship between the component parts is also not defined in the wire, which does not make it possible to stably provide the necessary stiffness of the wire for its introduction to a sufficient depth so that the maximum volume of metal in the ladle is captured by the reaction of magnesium with the melt. Uncertainty in the magnesium content in the flux-cored wire can lead to the formation of magnesium vapor inside the wire and rupture of the sheath at an insufficient depth and, as a result, to a decrease in the efficiency of magnesium use and the rapid course of the process.

The basis of the invention is the task of improving the wire for out-of-furnace processing of metallurgical melts by changing the composition of the filler wire by using magnesium not in the form of an alloy with silicon and iron, but in the form of a mixture with an alloy of silicon and iron, establishing certain optimal ratios and dependencies as between the components powder filler, and the entire 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, and reduce the size of the magnesium vapor bubbles. This will increase the degree of use of magnesium, ensure a consistently high level of desulfurization and modification, reduce wire consumption, significantly improve the environment during out-of-furnace treatment of cast iron, and produce cast iron with special properties.

The bottom line is that in a wire for out-of-furnace treatment of metallurgical melts, consisting of a metal shell and a powder filler containing magnesium, silicon and iron, magnesium is introduced into the composition of the filler in a mixture with an alloy of silicon and iron in the ratio (0.1 ... 1,2): 1, and the magnesium content in the composition of the wire is 8 ... 29 wt.%.

The essential features common with the prototype are:

- the composition of the wire from a metal sheath and powder filler;

- content in the powder filler of magnesium, silicon and iron.

Distinctive features of the prototype essential features are:

- the introduction of magnesium in the composition of the filler in a mixture with an alloy of silicon and iron in the ratio (0.1 ... 1.2): 1;

- the magnesium content in the composition of the wire is 8 ... 29 wt.%.

The distinguishing features given are necessary and sufficient for all cases to which the scope of legal protection of the utility model applies.

Between the essential features and the technical result - increasing the degree of magnesium use, ensuring a consistently high level of desulfurization and modification, reducing wire consumption, significantly improving the environment during out-of-furnace treatment of cast iron and producing cast iron with special properties - there is a causal relationship, which is explained as follows. When a flux-cored wire is introduced with a mixture of magnesium and an alloy of silicon and iron into the molten molten iron inside the wire, a chemical reaction occurs between the components of the mixture and an alloy of magnesium with iron and silicon is obtained. A large amount of heat is expended on the course of these chemical reactions, which is taken from the wire sheath, which, in turn, quickly heats up as it enters the melt. Thus, the melting time of the wire sheath increases significantly, which allows it to sink to a greater depth, and the maximum volume of metal in the ladle will be captured by the reaction of magnesium and melt. As was established by the studies, the time of melting of the metal sheath of the wire with filling with the finished ferrosilicon-magnesium alloy at a temperature of liquid cast iron of 1450 ° C is 2.0 s, and that of the same sheath of the wire with filling with a mixture of magnesium and an alloy of silicon with iron is 4.2 s. When using a wire of the given composition, the processes of magnesium release into the melt and melting of the filler alloy are synchronized over time, preventing the formation of magnesium vapor inside the wire or releasing the filler into molten iron in the solid state, since in this case, when the shell is melted, the magnesium alloy formed from the mixture will always be in a liquid state. Using 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. The alloy of magnesium with iron and silicon formed inside the wire is homogeneous and is released into the depth of the melt without local zones saturated with magnesium, or vice versa. 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 to slag. Magnesium dissolved in cast iron also reacts with sulfur, and the reaction products — magnesium vapor bubbles — are carried to slag. A certain ratio in the powder filler between magnesium and an alloy of silicon and iron [(0,1 ... 1,2): 1] allows to obtain a uniformly uniform alloy inside the wire. If the ratio limits between these components are not observed, the alloy will be inhomogeneous, some of its parts may be supersaturated with magnesium, and others may not be sufficiently saturated, which leads to a pyroelectric effect, emissions and unstable results when using wire. The magnesium content in the composition of the wire within the specified limits (8 ... 29 wt.%) Allows you to cover the entire volume of the ladle without emissions and sparging with the reaction of magnesium interacting with the iron-carbon melt, with a smooth desulfurization process and without the formation of local melt zones with excessive or insufficient magnesium content , which will lead to increased processing costs. All this can significantly increase the degree of use of magnesium for desulfurization, reducing dust and gas formation.

Thus, in order to significantly increase the degree of use of magnesium, to ensure a consistently high level of desulfurization and modification, to reduce wire consumption, to significantly improve the environment during out-of-furnace treatment of cast iron, and to obtain cast iron with special properties, it is necessary to use a wire of the specified composition with established optimal ratios and dependencies as between the composite parts of powder filler, and the whole wire as a whole.

A flux-cored wire is made as follows. The metal strip is profiled into a groove-like sheath. Dosed portions from two bins fill the shell with magnesium powder and silicon-silicon alloy, which are evenly distributed along the shell groove. Then, with the help of roller stands, they compress the shell and form a lock. Finished wire is wound on a spool and delivered to cast iron processing compartments.

составляет 76%. Процесс обработки чугуна протекал спокойно, без выбросов и барботажа. При использовании в таких же условиях проволоки, изготовленной по способу прототипа (содержание сплава в наполнителе проволоки: 25% магния, 62,5% кремния, 12,5% железа, наполнение проволоки - 100 г/м), конечное содержание серы составило 0,015%, а степень использования магния на десульфурацию - 45,6%, причем процесс обработки сопровождался пироэффектом и чрезмерным пылегазовыделением. Для получения равнозначного конечного содержания серы расход магния составят 0,42 кг/т или будет на 68% большим.At one of the metallurgical enterprises tested the inventive wire. The cast iron desulfurization unit / UDM / is supplied with molten cast iron in cast iron ladles (cast iron capacity of 100 tons), which are installed in staged places for processing. A flux-cored wire filled with a mixture of magnesium and a silicon-silicon alloy (magnesium - 35 g / m, a silicon-silicon alloy - 100 g / m, the ratio between magnesium and a mixture of silicon and iron alloy - 0.35, the magnesium content in the wire is 12%) using a tribribapart in liquid cast iron with a speed of 2.0 g / s. Conducted 10 treatments. The initial sulfur content in cast iron (S _p ) averaged 0.030%, the final (S _k ) - 0.005%, the consumption of magnesium (q _Mg ) was 0.25 kg / t. Extent of use of magnesium for desulfurization

is 76%. The processing of cast iron proceeded calmly, without emissions and sparging. When using wire under the same conditions according to the prototype method (alloy content in the filler wire: 25% magnesium, 62.5% silicon, 12.5% iron, wire filling - 100 g / m), the final sulfur content was 0.015% and the degree of use of magnesium for desulfurization is 45.6%, and the processing process was accompanied by a pyroeffect and excessive dust and gas emission. To obtain an equivalent final sulfur content, the magnesium consumption will be 0.42 kg / t or will be 68% greater.

Information sources

1. US patent No. 4205981, published 03.06.1980

2. USSR author's certificate No. 1655996, published on 06/15/1991

3. Patent of Ukraine No. 31893A, published December 15, 2000, bull. No. 7 - II.

Claims (1)

A wire for out-of-furnace treatment of metallurgical melts, consisting of a metal sheath and a powder filler containing magnesium, silicon and iron, characterized in that magnesium is introduced into the filler as a mixture with an alloy of silicon and iron in the ratio (0.1 ... 1, 2): 1 with a content of 8 ... 29 wt.%.