RU2195503C1 - Liquid steel heating method - Google Patents

Abstract

FIELD: ferrous metallurgy. SUBSTANCE: method involves heating liquid steel in steel-teeming ladle by introduction into steel melt of exothermal mixture comprising reducer - aluminum of mixture of aluminum and substance selected from group comprising calcium, magnesium, calcium silicon, and oxidizer - slag comprising iron oxides; blasting melt with inert gas. Exothermal mixture is introduced into melt in the form of filler of coated tube wire in an amount of 1.02-15.0 kg/t of steel at input rate of 1.44-5.8 kg/s. Method is used for heating metal to required temperature before pouring process and allows liquid metal to be heated in ladle at initial temperature insufficient for normal pouring in steel smelting or foundry shops lacking appropriate equipment and facilities for oxygen blasting of melt. EFFECT: increased efficiency and simplified method. 4 cl, 4 tbl, 1 ex

Description

 The invention relates to ferrous metallurgy, in particular to the production of steel and heating the metal to the desired temperature before casting.

 One of the important tasks of steelmaking is to obtain a metal that is homogeneous in properties in finished products, pipes and metal products. This goal is achieved using out-of-furnace treatment of melts in steel casting ladles. At the same time as refining the metal from harmful impurities during the out-of-furnace treatment, it is heated to a predetermined temperature, which ensures casting within the regulated temperature limits.

 Heating of steel during out-of-furnace processing increases the efficiency of steelmaking, as it allows to lower the temperature of steel output from the smelting unit, to stabilize the temperature of casting onset, which ensures an increase in the speed of casting of steel, a decrease in the limits of variation of the speed of casting within the same melting and, therefore, the production of ingots and cast billets with a more uniform and high-quality macrostructure and increase the productivity of continuous casting machines.

A known method of chemical heating of metal in a steel pouring ladle, which includes introducing aluminum wire into a liquid metal using a tribamer, dissolving aluminum and saturating the melt with it, blowing metal through an immersion lance with oxygen. See, for example, Chumakov S. M., Uryupin G. P., Zinchenko S. D. et al. Proceedings of the Fourth Steelmakers Congress. M. OJSC Chermetinformation. 1997, p. 295-296 [1]. To heat the steel at 1 ^o C, 0.04 kg of aluminum wire rod is introduced and technical oxygen is blown in the amount of 0.022 m ³ / t of steel, the rate of increase in metal temperature varies between 2-4 ^o C / min.

 The disadvantages of this method [1] are the additional costs of aluminum wire rod and oxygen; insufficiently high thermal efficiency (up to 75%) of metal heating; low resistance of the oxygen lance, which limits the process time and increases costs; relatively high capital investments in the construction of the oxygen station; increase in nitrogen content in steel; limiting the rate of metal heating by the diffusion rate of aluminum to the zone of interaction of the melt with an oxygen stream; equipment of special devices for exhaust gas and dust extraction.

Closest to the invention in technical essence and the achieved result is a known method of heating liquid steel in a ladle before secondary refining (Application JP 59-89708 Method for heating liquid steel (NIPPON SEITETSU K.K.) Japan. Claimed 15.11.82, 57-198940, published on 05.24.84, MKI C 21 C 7/00 [2]), consisting in the addition of exothermal materials (Al, Si, etc.) to steel from the hopper, blowing through a porous inert gas plug (Ar or CO ₂ ) for mixing, circulation of liquid steel and uniform distribution in her exothermic materials. At the same time, a small amount of O _{2 is} injected from above through a hollow tube immersed in steel, located exactly above the porous plug in the bottom, to conduct an exothermic oxidation reaction of the materials being seated and to heat the steel. Fluctuations in the level are insignificant and no emissions occur, therefore it is sufficient to have a free space height of 300-500 mm above the slag in the bucket.

The disadvantages of this method [2] are:
- additive in the steel from the hopper of exothermic materials (Al, Si, etc.), which due to the low density will be a significant time in the upper part of the melt in the ladle, which in addition to exothermic reactions with injected oxygen, causes the interaction of aluminum and silicon with atmospheric oxygen , components of slag on the surface of the melt and irrevocable heat loss through this surface;
- additional costs for oxygen and capital investments for the construction of an oxygen station, equipment for injecting oxygen into the melt and for drawing off exhaust gases and dust;
- low resistance of a hollow pipe for injecting oxygen into molten steel;
- increase the nitrogen content in liquid steel;
- the need to have a free space above the slag level of 300-500 mm.

The present invention eliminates these disadvantages. This is achieved by the fact that it is proposed to use a method of heating liquid steel, including smelting and discharging the metal into the ladle, fine-tuning the metal in the ladle, introducing exothermal material from the reducing agent (aluminum) and oxidizing agent into the steel melt, and blowing the melt with an inert gas, characterized in that aluminum and an oxidizing agent are introduced into the melt in the form of an exothermic mixture, which is a filler of a sheathed flux-cored wire, while an oxidizing agent containing iron oxides is used as an oxidizing agent at a ratio , wt.%:
iron oxide scale - 72-79
aluminum - 21-28
and the exothermic mixture is introduced into the melt in the amount of 1.02-15.0 kg / t of steel at a speed of 1.44-5.8 kg per second.

In addition, to increase the exothermicity of the mixture as a reducing agent, an additional material from the group is added to the exothermic mixture: calcium, magnesium and silicocalcium in the following ratio of components in the mixture, wt.%:
iron oxide scale - 72-79
aluminum - 21-25
calcium - 1-4
or
iron oxide scale - 73-76
aluminum - 21-26
magnesium - 1-3
or
iron oxide scale - 74-76
aluminum - 21-24
silicocalcium - 2-5
The proposed method for heating liquid steel in a ladle by introducing a flux-cored wire into it with filler from an exothermic mixture of the claimed compositions has several advantages. It is simple to implement, does not require large expenditures and production space, and can be carried out in steel mills in Russia, which do not have the ability to introduce oxygen into the ladle with a pipe (lance) and the ability to place complex equipment. The proposed method of heating liquid steel allows to reduce material and energy costs by eliminating the practiced overheating of the metal in the melting units, stabilizing the thermal regimes of steel casting.

The proposed method for heating liquid steel is based on the fact that when a sheathed flux-cored wire is introduced into the liquid steel with a filler from an exothermic mixture of scale powder and aluminum powder, the mixture interacts with the release of a large amount of heat inside the melt. According to Pliner Yu.L., Suchilnikov S.I., Rubinstein E.A. Aluminothermic production of ferroalloys and alloys. M., Metallurgizdat, 1963, p. 172-173, the thermal effect of the ΔН reaction per 1 kg of a mixture of Fe ₂ O ₃ and A1 is [3]:
_^2/3 Fe ₂ O ₃ + _^4/3 Al = _^4/3 Fe + ^{_2/3 of} Al ₂ O _3;
ΔH = 4019 kJ,
and mixtures of FeO and A1, respectively:
2FeO + _^4/3 A1 = 2Fe + _^2/3 Al ₂ O _3;
ΔH = 3203 kJ.

So, the total thermal effect ΔН from the interaction of iron oxide containing, for example, 69.5 wt.% FeO and 29.5 wt.% Fe ₂ O ₃ with aluminum will be
0.695 • 3203 + 0.295 • 4019 = 3395.6 kJ / kg.

 Given the stoichiometric ratios of the reactions of reduction of iron oxides with aluminum, as well as possible fluctuations in the composition of scale and aluminum, the filler of the flux-cored wire should contain, wt.%: Scale containing iron oxides, 73-79; aluminum 21-27.

 The introduction of an exothermic mixture in the form of a filler of a sheathed flux-cored wire in an amount of 1.02-15.0 kg per ton of steel improves the stability of the results and manufacturability of the process of heating the steel, and the feed rate of the exothermic mixture of 1.44-5.8 kg per second ensures its delivery deep into the melt, which contributes to better heat transfer and reduction, compared with the known method [2] (prototype), heat loss through the surface of the melt in the bucket. In this case, bubbling and fluctuations in the level of the melt in the ladle are less than in the known method [2], and the height of the free space above the level of slag required when introducing an exothermic mixture and blowing the melt with an inert gas for mixing is not more than 150 mm.

 The nitrogen content in the metal heated by cored wire according to the proposed method does not increase, while according to the known method [1] the mass fraction of nitrogen of steel grade 08Y increases on average by 0.0003%.

 Additional introduction of calcium, magnesium and silicocalcium flux-cored wire into the mixture of the filler wire, at the stated ratios of the components, enhance the exothermic effect of the reduction reactions of iron from oxides and promote the formation of oxide reaction products that easily float to the surface of the melt and are absorbed by slag. When high-activity and volatile elements — calcium and magnesium — are introduced into the filler of flux-cored wire fillers, better conditions are created for mixing the melt with vapor and, therefore, for intensifying heat transfer.

 Cored flux-cored wire with a diameter of 14-18 mm with a filler of an exothermic mixture of aluminum and scale powders, including with the addition of granules of calcium, magnesium and silicocalcium powder, is made on special mills using the well-known technology - Kablukovsky AF, Kamalov A.R. , Yaburov S.I. et al. Application of flux-cored wire for out-of-furnace steel processing. Metallurg, 1994, 1, p. 28-29 [4]. In the manufacture of cored flux-cored wire, dry mill scale powder with a particle size of not more than 2.5 mm was used. Before feeding into the hopper of the mill, the components of the exothermic mixture were weighed, observing the stated ratios, and thoroughly mixed. When mixing the respective components and producing flux-cored wire, contact with an open flame is not allowed. The wire coil is supplied with a document (passport or certificate) indicating the composition of the filler, including the mass fraction (%) of each component, the diameter of the wire, the mass of the coil and filler, the mass of the wire and filler in one running meter, the fill factor. The composition of exothermic mixtures of filler cored flux-cored wire are presented in table. 1.

To assess the degree of metal heating from the introduction of exothermic PP into the melt, we take the following density of substances (g / cm ³ ): aluminum - 2.69; FeO 5.70; Fe ₂ O ₃ - 5.25; PP steel shell (08Yu steel) - 7.8. The heat capacity of solid steel corresponds to 0.461 kJ / kg • deg. ; liquid steel - 0.772 kJ / kg • deg; heat of fusion of steel 259.78 kJ / kg.

 The characteristics of one running meter of flux-cored wires with fillers from the proposed exothermic mixtures, the level of thermal effects and the specific consumption of fillers for heating 1 ton of metal in a steel pouring ladle are given in table. 2.

 A specific application of the proposed method was carried out as follows.

Example 1. Steel grade 20 GOST 1050-88 was smelted in an arc furnace, released into a ladle with a main lining with a capacity of 100 tons and metal was refined in chemical composition. Then a thermocouple measured the temperature of the metal in the ladle, which was 1595 ^o C, which is lower than that required for casting in the range from 1600 to 1620 ^o C. Therefore, to heat the steel, a sheathed flux cored wire filled with an exothermic mixture was introduced into the melt through two streams by means of a tribeca containing, wt.%: dross of iron oxides 77 and aluminum powder 23 (table 1, mixture 1, table 2, mixture 1) in an amount of 6.7 kg / t with a wire feed speed of 230 m per minute, which corresponded to the speed introducing an exothermic mixture of 2.60 kg per second (table. 3, mixture (melting ) 1). After the flux-cored wire was introduced, the melt in the ladle was purged with inert argon gas for 2 min and the metal temperature was measured, which amounted to 1607 ^° C and corresponded to a predetermined interval. Then the metal was cast on a continuous casting machine.

 Similarly carried out the swimming trunks 2-13. The compositions of the mixtures used are given in table. 1, the characteristics of the cored wire in the table. 2, and the technological parameters and test results of the heating of liquid steel are presented in table. 3 and 4.

An analysis of the results shows that the method of heating liquid steel in a ladle according to the proposed technical solution at an exothermic mixture flow rate in the range 1.02-15.0 kg per ton of steel provides heating of the steel at 1-44 ^o C. Used for heating metal melts 2, 8, 11 at 1, 3 and 1 ^o С exothermic mixtures 2, 8, 11 (with the input parameters used in these melts) can be used to maintain the temperature at a given level; steel heating at 10-44 ^o C (melts 1, 3, 7, 9, 10, 12) with mixtures of 1, 3, 7, 9, 10, 12, with the appropriate input parameters, it is advisable to use to heat metal having a temperature below the permissible for casting.

With the same, with the known prototype method [2], level of heating at 20 ^o C (smelting 13), the consumption of aluminum in the smelting according to the proposed technical solution (smelting and mixture 9), equal to 2.12 kg per ton of steel, is less than smelting according to the known method of the prototype (2.6 kg per ton of steel). This indicates the advantage of introducing the exothermic mixture into the cored wire into the metal by means of a tribamer compared to the known prototype method [2], which involves the introduction of an exothermic material - aluminum from the hopper onto the melt surface.

Deviation from the proposed ratio of the components in the exothermic mixture leads to a deterioration in the heating process:
- a decrease in the content of scale in the mixture below the declared one, for example, as in melting (mixture) 4 (table. 3) to 71 wt.% (table. 1, mixture 4), at a rate of 1.1 kg / t of steel and the rate of introduction of the mixture 0.92 kg per second, it was not possible to obtain heating of the metal (steel cooled by 2 ^o C);
- an increase in the scale content in the mixture is higher than stated, for example, as in the smelting (mixture) 5 to 80 wt.% (table. 1, mixture 5), with a high consumption of the mixture of 15.2 kg / t of steel and a mixing rate of 3.54 kg per second, gives a smaller amount of heating (35 ^o C) than with the claimed composition on the heat (mixture) 3, which had a heating of 44 ^o C. This is due to the insufficient amount of 5 aluminum in the mixture (20 wt.%), which causes lowering its thermal.

The reduction in the melting (mixture) 6 of the consumption of the mixture to 0.9 kg / t of steel at a feed rate of up to 1.15 kg per second, that is, lower than the declared values, did not provide heating of the steel (the metal cooled by 1 ^o C).

 The maximum declared value of the filler input speed is assumed to be 5.8 kg per second, which corresponds to the input of flux-cored wire with a diameter of 18 mm through two streams of the tribamer at a speed of 300 m per minute. A further increase in the filler input rate is not technologically advanced. The maximum feed speed of flux-cored wire on existing tribing machines is limited to 300 m / min. The use of flux-cored wire with a diameter of more than 18 mm is fraught with technical difficulties in its manufacture and supply by the tribamer to the metal. The supply of the same type of material to the bucket simultaneously through more than two streams is not economically feasible.

 The additional introduction of calcium, magnesium and silicocalcium into the composition of exothermic mixtures in the declared amounts on melts (mixtures) 7-12 led, due to the interaction of calcium and magnesium vapor with the melt, to reduce the nitrogen content in steel (0.005-0.006 wt.%) (Table. 4) and better mixing of the metal, with less than in the case of the prototype, fluctuations in the level of the melt in the ladle (90-150 mm).

 By the nitrogen content in the steel (0.005-0.007 wt.%) And the magnitude of the melt level fluctuation in the ladle (50-150 mm), the heating of the melts 1-3, 7-12 (table. 4), produced according to the proposed technical solution, showed advantages in compared with the known prototype method [2], which had a higher smelting nitrogen 13 content (0.008 wt.%) and a melt level oscillation height of up to 280 mm when oxygen was blown into the metal.

 Thus, the use of the proposed technical solution allows for the heating of liquid steel in the ladle at an initial temperature insufficient for normal casting, in steelmaking or foundries that do not have the equipment and the possibility of heating by a known method [2].

Literature
1. Chumakov S. M., Uryupin G. P., Zinchenko S. D. et al. Proceedings of the Fourth Steelmakers Congress. M., OJSC Chermetinformation. 1997, p. 295-296.

 2. Application JP 59-89708 Method for heating liquid steel (NIPPON SEITETSU KK) Japan. Stated 11/15/82, 57-198940, published 05/24/84, MKI C 21 C 7/00.

 3. Pliner Yu. L., Suchilnikov SI, Rubinstein EA Aluminothermic production of ferroalloys and alloys. M., Metallurgizdat, 1963, p. 172-173.

 4. Kablukovsky A.F., Kamalov A.R., Yaburov S.I. etc. The use of flux-cored wire for out-of-furnace steel processing. Metallurg, 1994, 1, p. 28-29.

Claims (2)

1. A method of heating liquid steel, including smelting and discharging metal into a ladle, fine-tuning the metal in the ladle, introducing exothermic material from the reducing agent — aluminum and an oxidizing agent — into the steel melt, blowing the melt with an inert gas, characterized in that aluminum and an oxidizing agent are introduced into the melt is in the form of an exothermic mixture, which is a filler of the sheathed flux-cored wire, while dross containing iron oxides is used as an oxidizing agent in the following ratio of components in the mixture, wt. %:
Iron oxide containing scale - 72-79
Aluminum - 21-28
and the exothermic mixture is introduced into the melt in an amount of 1.02-15.0 kg / t of steel at a speed of 1.44-5.8 kg / s. 2. The method according to p. 1, characterized in that, as a reducing agent, calcium is additionally added to the exothermic mixture in the following ratio of components in the mixture, wt. %:
Iron oxide containing scale - 72-79
Aluminum - 21-25
Calcium - 2-4
3. The method according to p. 1, characterized in that, as a reducing agent, magnesium is additionally added to the exothermic mixture in the following ratio of components in the mixture, wt. %:
Iron oxide containing scale - 73-76
Aluminum - 21-26
Magnesium - 1-3
4. The method according to p. 1, characterized in that, as a reducing agent, silicocalcium is additionally added to the exothermic mixture in the following ratio of components in the mixture, wt. %:
Iron oxide containing scale - 74-76
Aluminum - 21-24
Silicocalcium - 2-5

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