DD285998A5 - METHOD FOR THE CONTINUOUS MELTING OF STEEL - Google Patents

Abstract

The invention relates to a method for the continuous melting of steel from at least largely prereduced Eisentraegern such. As pig iron and / or scrap, in which the melt is poured into a pan for subsequent metallurgical steps, the metallurgical slag by addition of Fluszmitteln on {process; Melt; Stole; Eisentraeger; pig iron; Scrap metal; Pan; Slag; addition; Fluszmittel}

Description

Process for continuous bleaching of steel Field of application of the invention

The invention relates to a method for the continuous melting of steel from at least largely prereduced iron carriers, such. B, pig iron and / or scrap, in which the melt is poured into a pan for subsequent metallurgical steps.

Characteristic of the known state of the art

For the production of steel from solid metallic iron carriers, in particular scrap, solid pig iron, pellets, sponge iron or mixtures thereof, oxygen uptake and Durchblaskonverter are usually used, wherein to achieve the required heat of fusion carbonaceous fuels are blown. The steel production from scrap, without the use of liquid pig iron succeeds without significant problems in electric arc furnace, but the cost of electrical energy in these cases is relatively high, eo.daß the economy of such processes is not readily given. In known converter method, in which oxygen is blown on or through the melt, can be worked faster and cheaper usually. However, such melting processes lead to relatively high proportions of oxides in the molten bath, and the slag produced in such processes usually has a relatively high viscosity. In addition, such highly viscous slags initially have inadequate permeability to the gas and may lead to excessive foaming and, if appropriate, to overcooking of the bath.

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Object of the invention

Ee let dae aim of the invention to bring a method of the generic type to apply, with a fast and inexpensive way of working is possible ·

Explanation of the essence of the invention

The invention has for its object «to provide a method for the continuous melting of steel from at least largely pre-reduced steel beams, with the excessive cooking reactions are avoided and the risk of foaming is significantly reduced. In addition, the subsequent refining or subsequent metallurgical steps in a ladle are to be facilitated by using the steal bath melted in this way and also to improve the iron output from the ladle. The object of the invention is essentially that the metallurgical slag by adding flux on

20-77.2 % FeO, especially 25.7-50 % FeO

10-30 % SiO ₂

2-15 % Al ₂ O ₃

5-20 % MgO

0.13-6.45 % MnO, especially 0.5-5 % MnO

1-10 % CaO

0.1-5 % Cr ₂ O ₃ ? + S tracks

is set. The fact that a metallurgical slag of this composition is set has

3X591 *

schenderrceiee demonstrated that in addition to the known change in viscosity by changing the slag composition, the mechanical gas permeability can also be favorably influenced. It has unexpectedly been shown that by adjusting the slag to the abovementioned composition, the foaming of the slag is suppressed in gas-forming metallurgical reactions can be, with such a slag beyond the condition provides ι subsequent metallurgical steps, such as exothermic reactions and / or make the exact adjustment of certain Si contents in steel bath »

Fe and Mn are mainly present in slag in the form of their monoxide FeO or MnO »

When pouring into a ladle, it is of considerable advantage if specific temperatures can be set in the molten steel and the metallurgical slag. "For the adjustment of certain temperatures, it is known to exploit silicothermal reactions in which necessary temperature increases can be achieved by the use of FeSi However, to be able to carry out such silicotherinic reactions without the risk of over-foaming and without the risk of an excessive cooking reaction, it is essential to provide a suitable metallurgical slag, which is also matched in its Vlekosltät and their mechanical gas permeability to subsequent silicothermal steps. In the context of the method according to the invention, it is therefore particularly advantageous if the procedure is such that the melt when pouring into the pan exothermically reacting additives such. B, Si, Al or * exothermically reacting alloys. By the present invention

slag guidance and the above-mentioned slag composition ee is now possible to control high slag amounts with a technically acceptable pan volume, the risk of overflow of the pans is avoided ·

In a particularly simple manner, as part of the erfindungsgemäößßn process as a flux compounds from the system FeO-MgO-SiO ₂ , such as. B, olivines or pyroxenes, are added, preferably foreterite, Mg-orthosilicate or Fe-orthosilicate are used as a flux. "In this way eich results in a targeted influencing the viscosity and the melting point of the slag, while a high gas permeability is achieved, which a foaming of the slag in the pan is reduced. Compounds from the system FeO-MgO-SiO _2, for example, olivines or pyroxenes have a high melting point per se. The reactions with very iron-rich acidic slags result in compounds with melting points Jm 1100 ° to 1200 ⁰ C, which is ensured at the usually prevailing temperatures a niedviekoee slag with high gas permeability. The use of such fluxes gives significant advantages compared to the conventional use of fluorspar, although fluorspar also converts lime to calcium silicate, however, the rate of reaction or recovery rate is significantly less when using for example. Forsterite, The energetically more favorable conversion reaction, such as It results in the application of magnesium and iron orthosilicates, resulting in a largely neutral slag, which ensures a longer life of the linings. The use of silicates,

in particular magnesium orthoilicate and iron orthosilicate, • in contrast to the use of fluorspar, does not lead to the formation of toxic and environmentally harmful gases *

The use of forsterite, which in itself has a high melting point, together leads to a significant reduction in the melting point of SiO ₂ , CaO, FeO and Ce ₂ O ₃ , in which case the resulting mixture of heat can be fully utilized. In turn, reaction with silicon results in further amounts of SiO ₂ , which delays the formation of dicarboxylic silicate and gives a low-melting monocalcium silicate.

Particularly in the case of over-remelted steel melts with iron-rich acid slags, the modification of the composition of the slag proposed according to the invention leads to the consequence of silicothermal reactions or exothermic reactions with a low tendency to foaming or overcooking. At the same time, the desired temperature can be relatively precisely determined The method is advantageously carried out in such a way that CaO is added to the pan before or during the casting. The pan is used as a template or added in the course of pouring CaO reacts with silicon according to the following equation

1 kg Si + 5.1 kg FeO + 4 kg CaO a 4 kg Fe + 6, kg (2 CaO, SiO ₃ ) +13816 kO

whereby a warming of the baths'verfolgen. By this reaction, on the one hand, the slag is heated, on the other hand, but at the same time the FeO of the slag, dae inevitable

The metal bath can be mixed by introducing argon through a purging plug on the bottom of the ladle in order to introduce the heat generated in the slag largely homogeneously into the metal and vice versa To avoid excessive over-heating of the pan, which could attack the pan-lining. "CaO amounts between 4 and 16 kg / t metal and Si between 2 and 8 kg / t metal are used with advantage, so that the eilikothermieche reaction can run optimally." A stoichiometric and quantitative conversion can be achieved by using CaO and Si in a mass ratio of approximately 4 to 1.

Slags of the following compositions have become particularly advantageous

54 % FeO 20 % SiO ₂

7 % Al ₂ O ₃

8 % MgO 3.9 % Mn

4 % CaO 0.8 % Cr ₂ O ₃

5 + P tracks

40 % FeO 20 % SiO ₂ 7 % Al ₂ O ₃ 8th % MgO - 3.9 % Mn 4 % CaO

0.8 % Cr ₂ O ₃ S + P traces

found,

Due to the slag guide according to the invention can be adjusted completely to the desired values using FeSi, in particular using FeSi (75 %), the silicon content of the Stahlbados "can be used with advantage so that in the molten steel, a content of 0.15 % - 0.40 % Si is adjusted by using FeSi.

A total of 18St through the slag guide of the invention perform the method so that with little overheating, especially with overheating in the pan prevented by addition of exothermic additives or at least delayed "The weakly overheated metal can in this case with an overheating of 10 to 30 C. run off from the S _c hrottschmelzgefäß and are cast together with the FeO-rich slag in the drip pan, Oie catch pan can be preheated to a temperature from 1500 to 1600 ⁰ C, "the desired temperature increase for further secondary metallurgical steps in the pan, allowing the Follow steps to perform degassing, LF treatment and further blowing in the converter with or without raw iron addition. During the filling process of the pan, FeSi (75 %) and lime can be added in a graduated manner or else the process is carried out so that lime is introduced as a template into the empty pan and FeSi (75 %) is added continuously »

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embodiment

The invention will be explained with reference to an embodiment nöher «

example 1

After demKVA method erfindungegemöß is 100% solid scrap use an overheated by 30 ⁰ C melt with slag mixed with an hourly capacity of 6> to 100 t into a standing below the melting vessel Auffangpfanrie whose capacity is 60 t crude steel liquid, enter left, "The Scrap may be added to iron and / or carburizing agents and / or metallic pellets. "For the overhead conduction of the melt, the silicothermal reaction with the FeO of the slag is used." Particulate FeSi (75 %) is used, which is applied to the slag as continuously as possible through a pan lid hole "17 kg of FeSi / t scrap are introduced, with the specific rate of addition (kg / min) depending on the set melting rate"

In order to be able to optimally run the silicothermal reaction (or the aluminothermic reaction), fluxing agents such as compounds from the system FeO-MgO-SiO ₂ (olivines, pyroxenes) or, by adding foreterite, Mg-orthosilicate or Fe-orthosilicate necessary, but which should attack the refractory lining of the collecting pan as little as possible. In addition, it is not desirable to have solid particles in the slag which are difficult to dissolve, such as CaO, since this tends to cause the treatment slag. to increase the CO evolution in the melt or the melt / slag boundary layer. The tendency to form foam coats which limits the CO or other gases produced

let pass "must therefore be avoided, since in / occur foaming or even effervescent slag the process must be interrupted. For this purpose, the treatment enamels are brought to a composition which is favorable for the wear of the socket and at the same time for the silicothermal treatment, by adding fluxes.

51 % FeO 20 % SiO ₂

8 % Al ₂ O ₃

6 % MgO

3.5 % MnO

4 % CaO

0.9% Cr ₂ O ₃

P + S traces and remainder iron

The addition of the flux in the amount of 12 kg / t scrap (controlled after the addition of FeSi and possibly CaO), the treatment slag is brought to the most favorable for the entire processes composition so that the silicothermal reaction with a versus a treatment slag without the said additions to an approximately 10 % improved thermal efficiency level expires, the aggressiveness of the slag is reduced to the refractory lining of the collecting pan (durability increased by about 20 %) and that no operational flow disturbing foaming or overcooking of the slag occurs, even if CaO is added. Otherwise, a CaO addition without addition of the above-mentioned fluxes until complete dissolution of the CaO certainly leads to boiling phenomena of the slag.

Example 2

After KVA Verfehren erfindungsgemöß is 100% solid scrap use an overheated by 20 ⁰ C melt with slag mixed with an hourly capacity of 60 to 100 t in sine standing under the Sohmelzgeföß catch pan whose Passungsvermögen is 60 t crude steel liquid allowed to enter · Dero Scrap may be added to iron and / or carburizing and / or metallic pellets. "The silicothermic reaction with the FeO of the Schicke is used for the upper conduction of the melt. In this process, powdered FeSi (75 %) is introduced into the intermediate layer metal / slag by means of an injection lance an inert inert gas is injected ·

12 kg of FeSi / t scrap are needed depending on the desired melt overheating, with the specific feed rate also being based on the set melting rate «

In order to be able to optimally drain the silicothermal reaction (or the aluminothermic reaction), fluxing agents such as compounds from the system FeO-Mg 2+ -SiO- (olivines, pyroxenes) or by the addition of forsterite, Mg-ortho-tellicate or Fe-orthosilicate necessary, but which should attack as little as possible the refractory lining of the collecting pan · In addition, it is not desirable in the slag solid particles. d.1.3 are difficult to dissolve, such as CaO, as this tends to froth the treatment slag in CO melt development or in the melt Z-slag boundary layer. The tendency to form foam slag, the limited cause CO or other gases pass, so it must be avoided at all costs, as the occurrence of foaming or even foaming slag

JiS

the process must be interrupted. For this purpose, the treatment slag is brought to a composition which is favorable for the wear of the socket and at the same time for the silicothermal treatment, by adding fluxes.

42 % FeO 20 % sio ₂ 7 9 & MgO 4 % MnO 4 % CaO 0 , 8 % Cr ₂ O ₃ P + S traces and rest iron

By adding the flux in the amount of 9 kg / t scrap (controlled after the addition of FeSi and possibly CaO), the treatment slag is brought to the most favorable composition for the entire operations, so that the sillkothermische reaction with a versus a treatment slag without the said additions to a by about 10 % improved thermal efficiency, the aggressiveness of the slag is reduced to the refractory lining of the collecting pan (durability increased by about 20 %) and that no operational flow disturbing foaming or overcooking of the slag occurs, even if CaO is added. A CaO addition leads without the addition of said flux until complete CaO dissolution otherwise with certainty to Kocherecheinungen the slag,

Claims (10)

, Berlin, May 18, 1990 71 198 24 claims Lu method for the continuous melting of steel from at least largely prereduced iron carriers, such. Example, pig iron and / or scrap, in which the melt is poured for subsequent metallurgical steps in a pan, characterized in that the metallurgical slag by adding flux on 20 - 77.2 % FeO, especially 25.7 - 50 % FeO is discontinued » 2. The method according to claim 1, characterized in that the melt when pouring into the pan exothermically reacting Zuechläge such. As Si, Ai or exothermally reacting alloys, are added. - 3. The method according to claim 1 or 2, characterized in that as a flux compounds from the system FeO-MgO-SiO ₂ , such as. As Oiivine or pyroxenes, are added. 4. The method according to claim 1, 2 or 3, characterized in that as a flux for adjusting the Schlackenzu- , Forsterite, Mg-Orthoeilikat or Fe-Orthosilikat is used. 5. The method of claim 1; 2; 3 or 4, characterized in that the melt is poured with an overheating of 10 - 30 ⁰ C and the solidification in the pan is prevented by the addition of exothermic reacting additives. 6. The method of claim 1; 2; 3; or 4, characterized in that in the pan before or during the casting CaO is added. 7. The method according to claim 6, characterized in that CaO and Si used in the mass ratio of about 4 to 1. 8. The method of claim 1; 2; 3; 4; 5; 6 or 7, characterized in that a slag of the composition 54 % PeO 20 % SiO ₂ 7 % Al ₂ O ₃ 8 % MgO 3.9 % MnO 4 % CaO 0.8 % Cr ₂ O ₃ 5 + P tracks is set. 9. The method of claim 1; 2; 3; 4; 5; 6, or 7, characterized in that a slag of the composition is set. 10. The method of claim 1; 2; 3; 4; 5; 6; 7; 8 or 9, characterized in that in the molten steel a content of 0.15 % - 0.40 % Si is adjusted by using PeSi.