CS272761B2 - Method of metal bath's slag composition checking in converter equipped with refractory lining - Google Patents

Abstract

This method of controlling a metal bath slag composition in a converter equipped with refractory lining is performed while purifying the metal bath slag by introducing gaseous oxygen in the course of the oxidation period and non-oxidising gasses in the course the reduction period, whereas this is followed by modification of the state of liquid mass so that the smelt has the pre-determined amount of aluminium oxide, silicic oxide, calcium oxide and magnesium oxide with the pre-determined ratio of aluminium oxide to silicic oxide in a ratio of about 0.1 to 10. The procedure includes six phases, whereas in the first phase aluminium and silicon are added to the bath as heating components in a combined share formed by 0 to 100 % by weight of aluminium and the residue of silicon, with the aim of increasing the temperature of the bath to the preset level and achievement of the given ratio of Al203 to Si02. In the second degree the weight of Al2O3 and SiO2 is modified after completing the first stage according to the mutual stoichiometric ratio between Al and Al2O3 and Si and SiO2 and the weight of Al, Al2O3, Si and SiO2, which are present prior to the first stage. In the third degree aluminium and silicon are added as reduction components with the purpose of carrying out full reduction. In the fourth stage silicon is added to modify the required state of the liquid mass. In the fifth stage the weight of Al2O3 and SiO2 contained in the smelt is modified according to their mutual stoichiometric relationship with aluminium and silicon and the weight of Al2O3 and SiO2 prior to carrying out the third stage; in the six stage calcium oxide and magnesium oxide are added in specific quantities for modification of the final state of the smelt.

Description

The invention relates to a method for controlling the composition of a metal bath slag in a converter provided with a refractory lining in a metal bath refining process, wherein oxygen gas is introduced into the bath during the oxidation period and non-oxidizing gases during the reduction period. to have a predetermined composition after completion of the refining process.

In some processes, the molten metal for refining carried out in refining vessels is conveyed. The molten metal may be any steel, such as carbon steel, low alloy steel, tool steel and stainless steel, and other metals such as nickel-cobalt based alloys. The refining operation generally consists of decarburizing the metal bath or melting and may also include adjusting the thermal regime of the metal bath (i.e., heating the bath), degassing, desulfurization and removal of entrained or entrained elements.

The process of the invention is one in which the decarburization and heating (or adjustment of the thermal regime) of the metal bath is achieved by injecting oxygen gas into the bath, preferably sub-sequentially, by the cell alone or in admixture with one or more gases from the argon group. nitrogen, ammonia, steam, carbon dioxide, hydrogen, methane or higher hydrocarbons. The gases can be introduced into the metal bath using various commonly used blowing programs depending on the type of steel and the specific gases used in combination with oxygen.

In carrying out the reduction operation, at least a portion of the metal bath is injected with non-oxidizing gases to aid in equilibrium, causing reactions between the slag and the metal.

The most commonly used method of metal refining in the steel industry is the argon-oxygen decarburization process known as the Ά00 * process. This process is described in various modifications in U.S. Patents 3,252,790, 3,046,107, 4,187,102, and 4,278,464.

During the oxidation period of this refining process, the metal bath is heated as a result of the exothermic oxidation being carried out. during the reduction and during the final treatment of the chemical composition, the bath is generally cooled, in cases where it is necessary to heat the bath at the beginning of the refining process, aluminum or silicon additives are used in conventional prior art to ensure the temperature rise of the metal to such an extent that the temperature is sufficiently high at the beginning of the reduction period and that the final stages of the refining process can be carried out.

After being transported to the refining vessel, the slag contains, in addition to the already formed slag, during transport also basic fluxes and consists of acidic oxides such as silica and alumina and alkaline components such as calcium oxide and magnesium oxide, other components which are contained in small quantities and which are not essential. During the refining process, further acidic oxides are formed and these oxides become part of the slag because during this process aluminum or silicon or their compounds, such as silicon carbide, are oxidized and the oxides formed contribute to the already present content of these substances. During the initial melt or oxidation phase, acidic components are formed by oxidizing all of the silicon contained in the metal to be transported and oxidizing the cell to aluminum, or silicon, or a mixture thereof, which are added to the metal bath as a heating component to heating bath). In the reduction period, acidic components are formed when aluminum or silicon is added to the metal bath to reduce other oxides from the slag.

The basic compounds, in particular calcium oxide and magnesium oxide, are normally added to the bath in the form of lime, magnesite or dolomite in fixed amounts according to the detected content of alumina and silica in the slag. These additives may be divided into individual batches, some or all of which may be added to the metal bath at the beginning of the refining process. For example, it may be noted that the

CS 272761 82 adds 3.8 parts of dolomite to each part by weight of silicon contained in the transported metal melt, or can be used as a heating component to heat the bath or as a reducing agent. which is available to the operator of the plant to determine the amount of additives to be added to the metal bath to adjust the chemical composition of the slag. When compounds such as calcium carbide are added and oxidized in the bath, basic oxides are also formed.

In the conventional refining process according to the prior art, the acid components supplied to the slag are largely selected according to the silicon content of the transported metal melt and the requirements for adjusting the thermal regime (i.e., heating the bath) and performing the reduction independently of the chemical composition of the transported slag. metal melts and slags. In parallel with or after the period of the period, silicon, which may be in pure form or in the form of compounds, is commonly added to the melt to adjust the final chemical composition to achieve a specified amount of silicon in the melt, independent of the chemical composition of the slag during reduction. Accordingly, the final chemical composition of the slag varies from melt to melt in the prior art.

The uncontrolled variation in the chemical composition of the slag has the following negative impact on the refining process, on the end product and on the vessel in which the refining process is carried out:

- the chemical composition of the slag decisively affects the ability of the slag to remove sulfur from the metal bath. The varying chemical composition of the slag therefore reduces the predictability of achieving a given final sulfur content in the metal. This results in either a less uniform achievement of the specified sulfur content in the metal, or in the use of slags which are excessively effective in their desulfurization capacity and consequently unnecessarily expensive or too expensive for the process.

- The wear rate of the lining of the vessel in which the refining process is carried out, in particular the magnesitochromite lining, is sensitive to the chemical composition of the slag in that changes in the ratio of alumina to silica in the slag influence the chemical corrosion rate of the refractory materials. . The cost of refractory materials can only be optimized by checking the equilibrium of all slag components.

In addition, if the wear rate of the lining cannot be predetermined, the chemical composition of the steel cannot be predicted either. The dissolution of magnesitochromite refractory material increases the content of iron and chromium oxides in the slag. These oxides, the increased amount of which results from wear of the lining, then react with the metal bath during the reduction period to form metallic iron and chromium in the metal phase and simultaneously oxidize the silicon from the metal phase. Therefore, to the same extent as the unpredictable extent of wear of the lining, there is also an unpredictable extent of loss of silicon from the metal bath and an increase in the iron and chromium content of the metal.

- Slag viscosity is a function of its chemical composition and temperature. Uncontrolled changes in the chemical composition of the slag thus affect the ease or difficulty of handling the slag, the efficiency of the refining process by mixing the slag with the metal and achieving an equilibrium state which is predetermined by achieving a certain content of alloy elements.

In summary, if there is no method of controlling the composition of the slag, or if the method is only imperfect, then its composition remains indefinite during the refining process. The indeterminate composition of the slag affects the ability of the slag to remove sulfur from the metal phase. This reduces the possibility of reaching a predetermined final sulfur content in the metal. The wear of the refractory lining in the converter also depends on the composition of the slag, and the changes in the composition influence the chemical corrosion rate of the refractory lining and thus the overall operating costs. The non-determinable wear rate of the refractory lining makes it also the indeterminate composition of the steel so produced. Dissolution of the lining components causes an increase in the iron oxide and chromium oxide contents in the slag, which then react in the reduction period to the metal iron and chromium in the metal bath, oxidizing the silicon x metal bath. The degree of uncertainty in the wear of the refractory lining also causes an indeterminate loss of silicon from the metal bath and an increase in the chromium content of the metal. The indeterminate composition of the Etruscan also affects the viscosity of the Etruscan.

It is therefore an object of the present invention to provide a control of the composition of the etruscan metal bath during refining processes of the metal bath in refractory lining converters in which oxygen is supplied to the metal bath during the oxidation period and non-oxidizing gases during the reduction period. the desired slag composition. This control of the composition of the Etruscan in said processes would eliminate the disadvantages of the prior art processes, the essence of the method of controlling the slag composition of a metal bath in a refractory lined converter in the refining process of the metal bath by introducing gaseous oxygen into the bath during the oxidation period and by introducing non-oxidizing gases and adjusting the state of the melt in such a way that the slag, after completion of the refining process, has a composition corresponding substantially to the following determined amounts of A wt. % Al2 Og, B wt. % SiO ₂ , C wt.%, CaO ca. MgO, wherein the ratio of alumina to silica is in the range of from about 0.1 to about 10.0, according to the present invention, is the addition of aluminum and silicon to the bath as a heating component to treat the thermal mode, ie. to heat the metal bath in a combined proportion of 0 to 100 wt. and the remainder is silicon, increasing the bath temperature to a predetermined level after completion of the oxidation period, achieving an alumina-silica ratio of A / B) in the second stage, adjusting the weight of the alumina and silica that are are present in the slag after completion of the first stage, according to the stoichiometric ratio between aluminum and alumina and between silicon and silica and the weight of aluminum, alumina, silicon and silica, which are present before the first stage) aluminum and silicon as reducing components at any point in time after completion of the oxidation period to achieve substantially complete reduction of the bath) in the fourth stage, silicon is added to the bath at the same time as or after the third stage, e.g. to obtain the desired melt state at the time of completion of the refining process) in the fifth stage, adjusting the weights of alumina and silica contained in the slag at the end of the refining process according to their stoichiometric relationship with aluminum and silicon and the alumina and silica weights present in the third stage) and in the sixth stage, calcium oxide and magnesium oxide are added to the bath to meet the following equations:

C

Cao -, AP ₄ + SP ₄ J7 - CP

A + B

MgO = ap ₄ + sp ₄ J

CTR

A + B in which it means

AP ^ weight of alumina in fifth stage,

SP ^ mass of silica in fifth stage,

CP and MP are the masses of magnesium oxide already contained in the slag,

CaO and Mgo are the corresponding masses of calcium oxide and magnesium oxide added in this sixth step, and

A, B, C and D are predetermined percentages.

Preferably, the weight of aluminum and silicon in the first stage is determined by calculating the desired weight of alumina to be formed from the aluminum as a heating component according to a smaller value obtained from the following equations:

H

X. / - + SP _X J - AP _t ^K 1

AF = -——- to ₂ + -. X

AF

H

in which AF is the mass of alumina obtained in the first stage from the addition of aluminum as a heating component,

AP ₁ is the mass of alumina present in the slag at the start of the feed of the heating components,

SP ₁ is the mass of silica present in the slag at the start of the feed of the heating components,

H is the value that corresponds to the temperature increase multiplied by the effective mass of the metal bath and the heat-resistant materials involved in thermal equilibrium, is the calculated constant representing the degrees of heat per unit silicon dioxide formed n unit of mass of the thermal equilibrium components according to the following equation:

Si / solid, 21 ° C_ / + 0 ₂ / “gas, 21 ° C_ / '= Si0 ₂ / slag, bath temperature / 7,

Kg 1 ^{e is the} calculated constant representing the heat, in degrees per unit mass of alumina, formed per unit mass of the components involved in the thermal equilibrium according to the following equation:

Al / pevný solid, 21 ° C + 3/2 0 ₂ / plyn gas, 21 ° C_7 ^e Al ₂ ° ₃ / Etruscan, bath temperature_ /, and X is the ratio A / B, whereupon the aluminum heating demand is calculated the stoichiometric component of the AF value, calculate the required weight of silica, which is obtained by adding silicon as the heating component, according to the following equation;

H - K ₂ . AF SF = • ^K 1 where / SF is the mass of silica obtained from silicon as the heating component, and finally the silicon requirement as the heating component is calculated from the stoichiometric conversion of the value for SF.

In a preferred embodiment of the invention, for the value of H, which is the product of the desired bath temperature increase in degrees Celsius and the weight of the temperature system in tonnes, all other weights are in kilograms, 15.6 and K ₂ is

17.6.

The process according to the invention makes it possible to achieve the desired slag composition, which has not been possible by prior art processes. The process of the present invention can be applied to the heat treatment stage (i.e., the heating of the bath by adding heating components) and / or to the melt reduction stage after / or to the finishing stage by adding a specified amount of silicon. These two last refining phases will be described in further detail below. The amount of the additives determined can be calculated in advance, with the addition being timed for the oxidation period, the reduction period or the finishing stage of the chemical composition, with optimum results being obtained by calculating the aluminum and silicon addition for each period.

The process of the present invention may be combined with a metal bath slag control process in a refractory lined converter in a refining process by melt reduction. This procedure is also applied when oxygen gas is introduced into the bath during the oxidation period and non-oxidizing gases are introduced into the metal bath during the reduction period, the slag having a composition corresponding to substantially A% by weight after the refining process. % alumina, B wt. % silica, c wt. % calcium oxide and D wt. magnesium oxide, the ratio of alumina to silica corresponding to a predetermined A / B value in the range of 0.1 to 10. This procedure is applied when there is no need to adjust the thermal regime of the metal bath, i.e. there is no need to add into the heating component bath. This procedure is performed as follows:

in a first step, aluminum and silicon are added to the bath as reducing components in a combined proportion of 0% to 100% by weight. the aluminum and the remainder are silicon to substantially complete the melt reduction and in relative proportions such that the ratio of alumina to silica in the slag is substantially A / B, in the second stage the alumina and silica weights present are adjusted in the slag after completion of the bath reduction, from the stoichiometric ratio between aluminum and alumina and between silicon and silica and the weight of aluminum, alumina, silicon and silica prior to the first stage, in the third stage silicon is added to the bath simultaneously with the first stage or after performing the first stage as necessary to provide the desired melt state upon completion of the refining process, and in the fourth stage, calcium oxide and magnesium oxide are added to the bath to meet the above-mentioned equations for calculating CaO and MgO.

The process of the present invention may also be combined either alone or in combination with the previous process with a method of controlling the composition of a metal bath etruscan in a refractory lined converter in a refining process by adding a specific amount of silicon to the heated melt. This process may be combined with one or both of the above processes where conditions are preferred. Also, this process of adjusting the composition of the etrusk by adding a specific amount of silicon to the heated bath is carried out in the oxidation and reduction periods as described above, achieving the predetermined levels of alumina, silica, calcium oxide and magnesium oxide in the slag. This procedure is performed as follows:

In the first step, the amount of specified silicon added to achieve the desired melt state after the refining process is calculated by multiplying the metal weight in the bath by the desired percentage of silicon in the bath after the refining process. % and the remainder is the silicon required to both achieve the specified silicon content in the first stage and to achieve a preselected X to A / B ratio according to the following equation:

Al + 3 SiO ₂ -> 2 Al ₂ 0g + 3 Si, in the third stage, adjust the weight of alumina and silica in the slag after completion of the second stage according to their stoichiometric relationship with aluminum and silicon and the weight of alumina and silica in slag prior to carrying out the second stage, and in the fourth stage, calcium oxide and magnesium oxide are added to the bath to meet the above-mentioned equations for CaO and MgO.

Preferably, the metal to be treated is selected from the group consisting of carbon steels, low alloy steels, stainless steels, tool steels, and nickel-cobalt-based alloys.

It is also advantageous in the process according to the invention if the refractory lining in the refractory converter is a magnesite-chromite material.

The process according to the invention is particularly suitable for applying to the ACO process as defined above, but it can also be applied to other converter processes, such as for example: KVOD, VODC, VOD and CLU! ¹ , and also applicable to the BOF and Q-BOP processes already disclosed in prior art patents when the reduction is carried out in a vessel into which a gas below the molten metal level is introduced to achieve equilibrium during the reduction. in general, the process of the invention is applicable to all refining processes in which the amount of each oxide formed in the slag can be determined by mass equilibrium calculations or statistical calculations and wherein the reduction of the etruscan is carried out in a refining vessel.

The refining process according to the invention thus comprises an oxidation period during which the decarburization takes place and the metal bath is completely heated, and a reduction period during which the oxidized alloying elements are reduced and / or the iron is reduced from alkaline etruscus. bath according to predetermined parameters for a given melt. The reduction period and final chemical composition is generally referred to as the oxidation refining process termination operation.

In the process according to the invention, the composition of the slag of the bath after completion of the refining process will be equal to the selected content, consisting essentially of A% by weight, of alumina,

% B, wt. % calcium oxide and D wt. magnesium oxide, wherein the ratio X of alumina to silica is a preselected value in the range of about 0.1 to 10.0. The preselected chemical composition at the completion of the refining is achieved by controlling the combined proportion of aluminum and silicon to achieve a predetermined ratio of alumina to silica in the slag, from as fully as possible determined values, while meeting the requirement to adjust the thermal regime. the heating of the metal bath, the reduction requirements and the final silicon content of the metal bath at given intervals, corresponding to the end of the oxidation period, the reduction period and the final treatment of the chemical composition. A predetermined amount of additives can be calculated in advance and the addition of the additives can be timed for the oxidation period or reduction period or for the chemical refinement operation, optimum results being obtained by calculating the aluminum and silicon addition for each period to achieve a preselected ratio of alumina to the silica at the end of the oxidation period and at the end of the reduction period and at the end of the chemical composition finishing stage, so that the melt after the refining process reaches a preselected slag composition.

However, in certain extreme situations, the combination of the initial slag and metal composition, the thermal regime requirements (i.e., bath heating), the reduction and the achievement of the specified silicon content, and the corresponding preselected chemical slag composition, may prevent the preselected chemical slag composition, despite the application of a combined additive of aluminum and silicon-like heating components added to the bath heating, reducing and adjusting the specified silicon content, for example, if the metal transported to the refining vessel contains a very high amount of silicon and component or reducing additive and the predetermined ratio of alumina to silica is very high, then even when adding mere aluminum while practicing heat treatment For example, the treatment (bath heating), reduction and finishing to achieve the specified silicon content by indirect addition of aluminum may not be sufficient to achieve the desired predetermined chemical composition of the slag. In such extreme and unusual cases, the use of the process of the invention would be the method leading to the chemical composition of the slag that is closest to a predetermined satisfactory chemical composition of all the possible results obtainable by the addition of combined proportions of aluminum and silicon.

Under these assumptions, it is also possible, and indeed more likely, that the preselected chemical composition of the slag may not be precisely achieved if a less advantageous embodiment of the process of the invention is used, especially if the process of the invention applies only to the treatment phase (i.e., the bath heating phase) or the reduction period itself. Accordingly, the term achieving a preselected chemical composition of the slag according to the present invention is intended rather to achieve the chemical composition of the slag as close as possible to the desired preselected chemical composition of the slag without the costs associated with the so-called two-slag process. By the two-slag process is meant replacing the slag in the refining vessel by completely or partially removing the slag from the vessel and then adding further slag-forming materials.

In the practice of the present invention, the control of the chemical composition of the metal bath slag in the refractory lining converter during bath refining is carried out by introducing oxygen gas during the oxidation period and introducing a non-existent gas during the reduction period. % constituted by substantially A wt. alumina, AlgOg, B wt.%, SiO ₂ , C wt. CaO and Dwt%, MgO, and the ratio X of alumina to silica having a preselected value in the range of 0.1 to 10, is proceeded as follows:

- in the first stage, the amount of aluminum and silicon to be added to the melt to heat it (heat mode adjustment) in a combined proportion of up to 100% aluminum and the remainder being silicon is calculated to effect the desired temperature rise of the metal bath after oxidation and achieving the desired relative ratio of alumina to silica at the end of the oxidation period, taking into account the composition of the slag and metal at the beginning of the oxidation period)

- in the second stage, the heating components, i.e. the aluminum and silicon compounds calculated in the previous stage, are added to the metal bath at any time during the oxidation period, oxidizing the added heating components)

- in the third stage, the mass of aluminum and silicon oxide is calculated in the slag after the second stage of the process)

- in the fourth stage, the amount of aluminum and silicon to be added to the melt as reducing agents in a combined proportion of 0 to 100% by weight, aluminum and the remainder being silicon is calculated to achieve a substantially complete bath reduction and desired alumina ratio X to the silica at the end of the reduction period with regard to the composition of the slag at the end of the second stage of the process)

- in the fifth phase, the calculated quantity of reducing agents determined in the fourth phase is added to the metal bath at any time after the decarburization has been completed)

- in the sixth stage, the expected mass fraction of alumina and silica in the slag after the reduction of the metal bath is calculated)

- in the seventh phase, the quantity of silicon to be added to achieve the desired proportion of silicon in the melt after completion of the refining process is calculated)

- if the expected ratio of alumina to silica is equal to the selected value of X after the reduction, then in the eighth phase, the amount of silicon calculated in the seventh phase is added to the melt simultaneously or sequentially with the fifth stage operation)

if the ratio of alumina to silica calculated in the sixth phase is less than the preselected value of X, then in the ninth phase, the proportion of aluminum in the range from 100 to 100% by weight is calculated. and the remainder is the silicon required to both achieve a specific silicon content in the melt and to achieve a preselected X ratio in accordance with the following reaction:

Al + 3 Si 0 ₂ 2 Al ₂ 0 ₃ + 3 Si

- in the tenth stage, aluminum and silicon, the quantities of which have been calculated in the ninth stage, are added simultaneously or after the fifth stage of the process,

- in the eleventh stage, the expected weight fraction of alumina and silica in the slag after the application of the eighth or tenth stages of the process is calculated,

- in the twelfth stage, calculate the amount of calcium and magnesium oxide to be added to the slag to achieve a preselected chemical composition of the slag based on the calculated alumina and silica weights present after the eleventh stage and the amount of these compounds already in the slag present, and

- in the thirteenth phase, calcium oxide and magnesium oxide, calculated in the twelfth stage of the process, are added to the melt at any time during the refining process.

Often the expected amounts of calcium oxide and magnesium oxide for a given melt are fed in advance to the refining vessel before the metal melt is fed into it. In such cases, the total requirement for the added amount of compounds calculated according to the present invention is reduced by the amount of pre-charged substances to the refining vessel from the calculation of the amounts of the subsequently added calcium oxide and magnesium oxide additives.

The following Tables 1 and 4 show a comparison of a prior art refining process carried out in a refining vessel by introducing oxygen gas below the bath surface and a process according to the invention.

C? »-“ »£ 5

ω

-p th>

as

-p ra

O 'P up tí Φ > » O rp ra O 05 / 'Φ O 44 O • P 8 φ OJ £} O O • H ω 'Φ s & φ ra rp lP tí O ra tí OJ '!> »-P rP ‘ í>. ra pj > 5 tí £ í 05 / 05 / tí W PU £> Φ 'tí O

hO • p 44 ω \ 'Three

OJ ra o

O <d iP

O

CL '05

Ή 0) th O Φ 44 73 \ <y nj QÓ> 'Φ 44 Th

JP &

• • P > o 05 / tí 0) í> 05 / P Ό) 44 {> O rP !> O tí 44 £ J Φ O 05 / 05 / tí ΕΊ * P P 05 / tí PU tí P ra O fk

Ή Ή 44 o '05 p>

P '05 '> s 44

Ό th Φ · Ρ CU Ή bp th> th © '05 44 ø PU P rp \ '&

!>

es +>

tí o

PU ra £

PU tí

P ra o

fk • P ca

£>

O

rp p- CU. rp CM CM CM CM p * · WHAT rp; of alcohol rp rp rp rp σ \ · OJ rp WHAT OJ - rp in Ch «** WHAT rp. τ- · p- CM » • P • P • r-i • r-f ω ω what ca v-. * - * r ~ <s •in Λ r » what - WHAT 00 · what r— > P • P ip H ω ω <4 <? σ \ Ch rp. rp r \ - of alcohol tn r- C- rP rp ip iP < <5 <5 • 4 p- - 00 p- WHAT »« WS · * IF \ ir\ P-. (P p · rp in- p- P- ** »* *to O O O O < ffl O β

*> ϋ what

Η

Χ5

Φ

Εη φ

05 '05 three £

Ο

Λ

Ό tí

V rd

Φ

Φ rtí

Ό

Ρ.

á ⁹ ω

-ρ ω

φ> Ν ©

Η ©

Η ο

Ρ • í th ο

ω>

Η φ

>

• Ρ 'Φ>

Ο ί>

©

Φ

Ο

C0 three Η Η <Ρ three

Ρ.

-Ρ w

©

ΡΜ

• rl what Ό5 <P WHAT 3 Φ l> Λ > WHAT WHAT tí ω 3 Pi I '3 ©

• Η ω

him

• tí • rl • rl rtí • rl WHAT what what <4 what T— r- · r- tn CSX r. *% Λ ** 00 00 OO · O

O Pi Φ O Ή 44 tí Φ £ Ό Φ 44 Φ £ & tí \ 'Φ Ή 44 tí ϋ xo rtí ♦ rl i> O • P '05 44 Ό tí WHAT • rl Pi tí > tí © ftí Pi -P

φ Ρ Χθ <—I

Ο 05

Ο \ 'Φ Λ!

tí w Φ 3 H tí CM O P O> f> w • Ϊ Ϊ & 'tí CO \ and tí n φ Φ ό > N O φ G CM \ > tí r-l H pm 03 / <4 \

Θ • í th ©

Ρ, ω

tí ra δ

rtí £>

© 'hb

Ρη

rtí • rl t — 1 • tí H .. «? • rl WHAT <4 what <4 what , *. xt tn xt . in σ \ r » Λ • t · » · * tn in- x | - T- Xť ·

rtí • rl rtí • rl rtí • rl <4 what <! WHAT what c- ~ • VO · O- O tn σ \ - Λ «« · * !> - and- 0-  * ς $ · xť - o m 04 · Xt in

, 8 Al 7.3 Alΐη ιη ιη

CM ιη

F Ο Ο xf-. xJ- χΓ

VO KD C— οί η;

σχ σχ

00 χ} 00

- ’ι t-J * 4 <4 OQ U

In the comparison procedures, the results of which are shown in Tables I and IX, the composition of the transported metal was essentially the same except for the silicon content in the transported metal, which differed in the same way for procedures A and B and for procedures C and D in both sets. of the present examples. In all processes, 4,536 kg of metal were refined and the melts were initially free of alumina, silica, calcium oxide and magnesium oxide. The other oxides present in the form of iron oxide, manganese oxide and chromium oxide, which must be reduced to pure metal in the reduction stage, contained 6.8 kg of oxygen. The determined silicon content at the end of the refining was 0.40 wt%. In all cases, an increase in the temperature of the metal bath by 222 ° C was also required, and it was also assumed that 2,948 kg of refractory materials and substantially no slag were involved in the thermal reactions in the prior art , the results of which are shown in Table I, show insufficient control of the chemical composition of the slag expected by the refining of the metal bath by injecting oxygen into the bath, particularly in the case of refining carbonaceous and low alloy steels. In all cases A to D in the procedures of Table I, guidance on the determination of the amount of calcium oxide and magnesium oxide to be added to the slag is based on established practice in which 3.8 kg of dolomitic lime is added per kg of silicon in the transported metal, the heating components or the reducing agent, by 1.02 kg of dolomitic lime per 1 kg of aluminum, which is added as a heating component or as a reducing agent. Dolomitic limestone consists of 60 wt. In all four cases A to D, an equivalent degree of temperature increase was required to adjust the thermal regime of the bath, with the addition of aluminum as a heating component in addition to the initial silicon content, in cases B and D higher silicon contents in the metal to be transported provided a higher content of heating component and therefore less aluminum was required than in cases A and c. The procedures of A and B illustrate the case in which silicon is used for reduction. The unplanned variation of the silicon content of the transported metal in processes A and B causes a change in the alumina content of the slag by 16% by weight, silica by 13% by weight, calcium oxide by 2% by weight. and magnesium oxide by 1 wt. Similar changes in chemical composition occur in cases C and D, where the reduction was performed by the addition of aluminum instead of silicon.

In contrast to this prior art process, according to Table II, which illustrates the process of the invention, the chemical composition of the slag is preselected and the additives of heating components, reducing agent and silicon to achieve this predetermined content of the individual components in the slag are determined for to achieve this chemical composition of the slag, while at the same time meeting the requirements for performing a reduction, adjusting the thermal regime (desired temperature increase) and adjusting the specific silicon content.

Methods for determining the overall process needs in terms of adjusting the thermal regime and performing the reduction, i.e. determining the temperature and heat capacity of the system and determining the amount of oxygen to be reduced in the reduction period, are generally apparent to those skilled in the art. in the description of the invention. However, the practice of the present invention does not depend on the precise determination of the thermal regime of the metal bath, i.e. the temperature of the metal bath. determination of bath temperature increase. If the need to increase the bath temperature is determined inaccurately but the process of the invention is carried out correctly, the resulting slag will still correspond to a predetermined final composition and the resulting silicon content will coincide with the predetermined silicon content, but the metal bath will have an unsuitable tapping temperature tavby. Therefore, corrective action would have to be taken to adjust the temperature of the bath according to the invention, or otherwise.

Processes A and B in Table II illustrate methods by which, according to the invention, slag can be produced with relatively low desulphurization capacity and low corrosivity for magnesium-chromium refractory materials independently of unplanned changes in the silicon content of the transported metal. Processes C and D illustrate methods by which a slag having a strong desulphurisation capability can be achieved, the slag also having low corrosion to magnesite-chromite refractory materials with the same variations in the silicon content of the transported metal. In process D, the specified silicon content is achieved in the final treatment of the chemical composition by the addition of silicon and aluminum.

In the process according to the invention, a combined addition of 0 to 100 wt. of aluminum, the remainder being silicon, both to provide an increase in the temperature of the metal bath (heat mode adjustment) as well as to reduce the bath and to achieve a preselected chemical slag composition which represents A% by weight. % alumina, B wt. % silica, c wt. % calcium oxide and D wt. magnesium oxide at a specific ratio of alumina to silica A / B ranging from 0.1 to 10.0. The selection of the optimum percentage of each slag component for a preselected slag composition at the end of the refining process is not within the scope of the present invention.

The resulting slag consists essentially of the following components: alumina, silica, calcium oxide and magnesium oxide, the other components being of minor importance. For the sake of simplicity, it is believed that the four components comprise 100 wt. slags. However, even when these four components make up less than 100% by weight. slag, this process is within the scope of the present invention, although the process of the invention has been described by first performing a bath heating phase (adjusting the thermal regime of the metal bath), then reducing and finally adjusting the chemical composition, Any of the three steps may be performed more than once during refining of the metal. For example, the batch can be heated and then reduced, and then reheated and reduced, after which the chemical composition is finally adjusted. Various variations in the performance of the chronological sequence of the steps, including the possibility of repeating the individual steps, do not limit the scope of the invention and its applicability, but the further description of the process of the invention will be limited to the preferred chronological sequence of the steps.

The first stage of the process of the present invention is carried out during the oxidation period and involves adding the calculated amounts of aluminum and silicon required as heating components to achieve the desired temperature rise of the metal bath after the oxidation period is added at a rate that is suitable to achieve the ratio X of alumina to silica at the end of the oxidation period with respect to the metal and slag composition at the end of the oxidation period; in the process of the invention the alumina to silica ratio at the end of the oxidation period is close to a predetermined chemical composition; however, it may not exactly match this composition.

The same applies to the reduction period, taking into account that the process according to the invention allows the final adjustment of the chemical composition, which is carried out in a predetermined manner, at which the desired ratio of aluminum oxide to silica is achieved. In the process of the invention, any of the commonly known methods can be used to calculate the amount of the added heating components during the oxidation period, thereby limiting the process to control the chemical composition of the slag in the reduction period and the final adjustment of the chemical composition. In this modified process according to the invention, the addition of the heating components is calculated as a combined fixed proportion of 0 to 100% by weight. aluminum, the remainder being silicon, which is used to adjust the thermal regime of the metal bath (effecting the desired bath temperature increase), and then adjusting the chemical composition of the slag by adding a predetermined mixture of aluminum and silicon in the reduction period and adding silicon in the final phase modification of the final composition of the slag, as will be discussed below. The proportion of aluminum and silicon used as heating components in the oxidation phase of this modified process of the invention is the same for all processed melt, irrespective of the silicon content of the transported melt and the need to adjust the thermal regime of the metal bath. wherein the solid combination should be such that the slag formed at the end of this melt heating stage has an adjustable composition to a predetermined chemical composition.

For various reasons, a different X ratio can be chosen for each of the three refining stages, indicating the ratio of the amount of alumina to silica. For example, in cases where the added heating component is oxidized prior to decarburization of the metal bath, a lower ratio of alumina to silica may be selected at the heat treatment stage (when the metal bath is heated) to avoid discharge from the converter, a higher ratio of alumina to silica may be chosen to achieve greater desulfurization.

similarly, a conventional reduction period may be used in an alternative embodiment, thereby limiting the method of controlling the chemical composition of the slag to only the final phase referred to herein as the final adjustment of the chemical composition of the slag, or to a combination of control at this stage and oxidation period. In other words, the process of the present invention need not be applied to the final phase alone; for the final setting of the chemical composition of the slag, or only for the oxidation period or only for the reduction period, but can be applied at any of the refining stages or in any combination of any of the refining stages. According to the present invention, however, it is preferred that the slag composition is controlled during the oxidation period and the reduction period in addition to the final adjustment of the chemical composition of the slag.

A preferred embodiment of the process of the present invention will be illustrated by the following detailed description of the various phases of the process:

1.1 The required chemical composition of the slag is A% by weight. % alumina, B wt. % silica, c wt. % calcium oxide and D wt. magnesium oxide, with:

A + B + C + D - 100% and A / B = X = 0.1 to 10.0.

1.2. Calculate the mass of aluminum and silicon as added heating components to adjust the thermal mode of the metal melt (required increase in bath temperature) during the oxidation period and to achieve the ratio X of alumina to silica, according to the following equations and of these equations i

H

X. - + SP ₁ J ^K 1

AF ----- ^K 2 + -. where in these equations means

AF weight of alumina obtained in the first stage from the addition of aluminum as a heating component,

APg is the weight of alumina contained in the slag in the oxidation period prior to the addition of the heating components. This value is equal to the weight of aluminum introduced into the cell refining vessel as part of all the charge metal, or as an additive multiplied by 102/54 plus the weight of aluminum introduced into the transported slag refining vessel,

SPj is the mass of silica contained in the slag in the oxidation period before the addition of the heating components. This mass is equal to the mass of silicon introduced into the refining vessel in the transported metal plus the mass of silicon introduced through the added alloys times 60/20 plus the mass of silica introduced into the refining vessel with all the transported etrusk,

H is the temperature increase multiplied by the effective mass of the metal and etruscan bath and the proportion of refractory materials involved in the thermal equilibrium, taking into account the necessary temperature rise to be carried out to heat the melt from the initial temperature to the desired final temperature at this stage of refining, taking into account the heat losses occurring during the heating of the metal bath and the cooling effect of any additives added to the refining vessel,

K i is the heat in degrees per unit mass of silica formed from the unit mass of the components involved in the thermal equilibrium according to the following equation:

Si solid, 21 ° CJ + 0 ₂ £ gas, 21 ° CJ = Si0 ₂ / Etruscan, bath temperature _ /

K ₂ is the heat in degrees per unit mass of alumina formed from the unit mass of the components involved in the thermal equilibrium according to the following equation:

Al f solid, 21 ° C + 3/2 0 ₂ / gas, 21 ° C - ^a ^ 2 ° 3 ^{slag <a} / bath temperature J, a | < ₂ are constants of preferred values 15.6 and 17.6 for H as the value obtained by multiplying the desired increase in the temperature of the metal bath in degrees Celsius by the weight of the heating system in tonnes, the other masses in kilograms *

- once the AF value is calculated, then the amount of aluminum as the heating component to be added to the bath is equal to the AF value multiplied by 54/102 minus the amount of aluminum already contained in the metal,

- the quantity of silica to be produced by the addition of silicon as a heating component is given by:

H - K ₂ . AF

SF where SF is the mass of silica obtained by adding silicon as a heating component and the other symbols have the same meaning as above,

- once the SF value is calculated, then the amount of silicon as. the heating component to be added to the melt is equal to DF times 28/60, minus the weight of silicon already present in the metal.

1.3. Aluminum and silicon are added to the melt in the calculated combined fraction as heating components, the additive being carried out at any time during the oxidation period to oxidize the heating components.

2.0 The second step of the process of the invention involves calculating the amount of alumina and silica produced by reducing the metal bath to achieve a substantially perfect reduction and achieving the desired alumina-silica ratio X in the slag after reduction, taking into account the chemical composition of the slag after the end of the oxidation period. For the purposes of the present invention, the reduction is considered to be substantially complete when the iron, manganese and chromium oxides are substantially completely reduced to the metallic form of these elements. This calculation is preferably performed as follows:

2.1. The amount of alumina in the delivery period is calculated AP ₂ on the SP ₂ silica contained in the slag for oxina based on the following equations: ap ₂ = ΑΡ _χ + AF sp ₂ = SP ₁ + SF

2.2. Calculate the amount of aluminum and silicon required to reduce the metal bath and to achieve the ratio X of alumina to silica. The required amount of alumina to be produced during the reduction of AR is given by the following equations:

R

X. C - _{+ c} SP ₂ J - AP ₂

AR

AR - in which R is the oxygen content of the slag to be reduced by reaction with aluminum and silicon? calculated by subtracting the amount of oxygen that oxidizes aluminum, silicon or carbon from the total amount of oxygen introduced into the melt during processing,

Kg is the mass of oxygen reduced by the formation of one mass unit of silica in the slag? preferably the Kg value is 32/60,

K ₄ is the mass of oxygen reduced to form one mass unit of alumina? preferably K ₄ is 48/102.

2.3. The amount of aluminum to be used as reducing agent SR corresponds to:

SR = AR. 54/102.

2.4. The amount of SR silica obtained during the reduction is given by:

R - K ₄ . AR SR = ^K3

2.5. The quantity of silicon to be used as reducing agent corresponds to an SR value of 28/60.

2.6. Add a calculated amount of aluminum and silicon as reducing agents to achieve substantially complete melt reduction at any time after decarburization.

3.0. The third stage of the refining process involves calculating the amount of alumina recovered and the amount of silica to be reduced from the slag at the stage of addition of a specific amount of silicon to achieve a specific silicon content in the metal and achieve the desired ratio of alumina to silica in the slag. adding a specified amount of silicon, taking into account the amount of these oxides present in the slag prior to addition of the specified amount of silicon.

This stage is referred to as the finishing of the chemical composition of the slag, based on two considerations:

□ if the ratio of alumina to silica is the desired X value before addition of the specified amount of silicon, then the specified amount of silicon can only be achieved by adding silicon to the melt. (However, if the ratio of alumina to silica is less than a preselected value of χ, then the specified silicon content at the end of the process will not be achieved by adding only silicon to the melt, as is conventional practice, but by a combination of silicon and aluminum.

When mixed with silica-containing slag, the aluminum additive will react according to the following equation:

Al /%, metal J + 3 Si0 ₂ £ ~ slag _ / = 3 Si%, metal _ / + 2 Al ₂ 0 ₃ slag J

The above reaction causes the added aluminum to convert to alumina in the slag to produce the specified silicon content in the metal and reduce the silica in the slag, the only result of which is to increase the ratio of alumina to silica.

For the calculation of the specified amount of silicon added directly as silicon and indirectly as aluminum, the following procedure is preferred:

3.1. Calculate the APg and SP ₃ values, which are the weights of alumina and silica in the slag after the reduction stage:

Pg = AP ₂ + AR

SP ₃ ° SP ₂ + SR

3.2. Calculate the amount of alumina to be formed in the slag to provide the specified amount of silicon in the melt according to the following equations, taking the smaller value obtained from these equations with

X, SP ₃ - and ap ₃

AS ^K 6 + -. X

WITH

AS = ^K 6 where means

AS weight of alumina in the slag as a result of the addition of aluminum to indirectly provide the specified silicon content,

S the total mass of silicon required to achieve the specified quantity of silicon in the melt, calculated in a manner known per se,

K ₅ is the mass of silicon formed in the melt by reducing one mass unit of silica from the slag / preferably has a Kg value of 28/60,

Kg is the mass of silicon formed in the melt of metal per mass unit of alumina resulting from the indirect silicon additive j

Al + 3 SiO ₂ = 2 Al ₂ 0 ₃ + 3 Si j, preferably having a K _&amp;

3.3. The quantity of aluminum to be used for the indirect delivery of the specified quantity of silicon is equal to AS times 54/102.

3.4. The amount of SS silica produced by the addition of a specified quantity of silicon is given by the equation:

“ ^K 6

SS = -. AS where SS is a negative value indicating that the silica has been reduced.

3.5. The amount of silicon to be used as direct additive to achieve the specified quantity of silicon is given by the equation:

PS / weight of silicon to be added / - s + _. ss, and since ss is a negative mass value of the silicon to be added, it is

PS less than s, which is the total amount of silicon as additive.

3.6. A mixture of aluminum and silicon is added to the melt to form alumina and to reduce silica, which was calculated in accordance with paragraphs 3.3 and 3.5 at any time after decarburization has been carried out,

3.7. Calculate the total amount of alumina AP ₄ and silica SP ₄ in the slag after completion of the procedure in paragraph 3.6 according to the following equation;

₄ AP = AP + AS ₃ sp ₄ «SP ₃ + SS

4.0. Calculate the amount of calcium oxide and magnesium oxide to be added to the slag to achieve a predetermined content of aluminum oxide A% by weight, silica B% by weight, calcium oxide C% by weight. % and magnesium oxide D wt. based on the calculated weight of alumina and silica after adjusting the specified amount of silicon,

Preferably, the following equations are used to calculate the amount of calcium oxide and magnesium oxide to be added to the slag to achieve the desired chemical composition of the slag;

C cao B -. / AP ₄ + SP ₄ / - CP

A + B □

Mgo = -. / AP ₄ + SP ₄ / MP

A + B where A stands for A,

CPs are already included in

B, C and D predetermined percentages, and MP are the weights of calcium oxide and magnesium oxide that slag,

AP ₄ is the mass of alumina adjusted in the third stage,

SP ₄ is the weight of silica treated in the third stage.

Calculation of the mass amounts of lime, dolomite and magnesite to be added to the metal bath to match the amount of calcium oxide and magnesium oxide in the slag is performed by conventional stoichiometric conversion and need not be reported here.

4.1. The calculated amounts of calcium oxide and magnesium oxide referred to in paragraph 4 may be added to the melt at any point in the refining process, and multiple additions may also be used.

It will be apparent to those skilled in the art that steps 1 to 4 of the process of the invention may be calculated prior to carrying out a refining operation for a transported melt of known composition, and the calculations may be performed by computer. The operator only needs to introduce a predetermined amount of aluminum and silicon into the metal melt at the appropriate time in the individual stages of the refining process.

The principles of slag formation with a predetermined chemical composition while meeting the requirement to adjust the thermal regime (i.e., heating the bath with the addition of heating components), to perform the reduction and to perform the desired silicon additive to the melt are utilized in three separate stages. the addition of aluminum and silicon to the melt can be made interchangeably as a result of calculating the combined proportion of alumina and / or silica formed in slag or reduced from slag. Each of the three steps in which the combined addition of aluminum with silicon as additives is within the scope of the present invention. According to a preferred embodiment of the process of the invention, aluminum and silicon are added in calculated combined proportions to each of the three stages of the refining process. However, the advantages of the process of the present invention can be fully or substantially fully achieved by using one or two of the three steps in which the calculated combined aluminum and silicon content is added, while other conventional methods of combined aluminum addition may be applied in the other steps or steps. and silicon not within the scope of the present invention.

For example, to obtain a slag of a predetermined chemical composition, it would be possible to add aluminum and silicon as heating components in a fixed ratio, regardless of the initial chemical composition of the slag and metal or the overall demand for the heating components to achieve the desired thermal regime. heating the bath to the desired temperature, but not to achieve a predetermined chemical composition of the slag or the desired ratio of alumina to silica. The resulting chemical slag composition at the end of the heat treatment period (i.e., heating the bath to the desired temperature with the fuel additive) can be adjusted to achieve a preselected chemical slag composition during subsequent refining using the method described above for calculating the aluminum and silicon additive period and for the stage referred to as the specified silicon content setting.

Similarly, it is possible to determine in advance whether the melt is to be reduced and to perform this reduction using a fixed aluminum to silicon ratio, but this fixed aluminum to silicon ratio is not determined by the method of the invention. The combination of aluminum and silicon added to adjust the chemical composition of the slag to a predetermined composition is already carried out according to the invention, taking into account the chemical action of the reducing agents on the chemical composition of the slag. It is believed that in a number of instances, given the initial conditions, with a preselected chemical composition of the slag and a preselected reduction and thermal mode requirement, the application of the process of the invention allows the thermal mode adjustment (i.e. bath heating) and reduction stage. addition of silicon in a conventional manner to achieve a specified silicon content without the use of indirect aluminum addition. Furthermore, it is possible that in certain cases where only one stage according to the invention is applied and where the combined proportion of aluminum and silicon is calculated as a fuel addition in the first stage, in the reduction stage or in the treatment stage of the specific silicon content setting the slag to a predetermined chemical composition, while in other steps, aluminum and silicon combined addition processes not within the scope of the present invention may be applied.

Hereinafter, an exemplary embodiment of the process of the present invention will be described.

Example ‘

According to this procedure, a batch of g 072 kilograms of metal was transported to a converter vessel containing 45.3 kilograms of slag consisting of 30% by weight. silica, 10 wt.%, alumina, 50 wt. % calcium oxide and 10 wt. magnesium oxide, and 4.54 kilograms of silicon contained in the metal. In this procedure, the reduction was carried out with equal amounts of aluminum and silicon. It was assumed in the batch that it was necessary to reduce

4.5 kg of oxygen from the bath so 2.27 kg of aluminum and 2.27 kg of silicon were added to complete the reduction. In this procedure, the specified amount of silicon was added in the form of ferrosilicon, which did not affect the slag composition. Assuming hundreds of isometric relationships, the composition of the slag was calculated as follows: 28.6 kg of silica, (3.61 kg of transported slag, 9.53 kg of oxidation of transported silicon and 4.99 kg of silicon additive reduction), 8.62 kg aluminum oxide (4.54 kg of transported slag and 4.08 kg of aluminum additive reduction)

22.7 kilograms of calcium oxide and 4.54 kilograms of magnesium oxide (both of these oxides from the transported etruscus), except for the content of these substances coming from the heat treatment stage (i.e., heating the metal bath).

At a given melting of 9,072 kilograms of metal, 45.4 kilograms of slag and an estimated 3,584 kilograms of refractory material must be heated by 111 ° C by the addition of heating components, the requirement to achieve the final composition of the slag was as follows: 24 wt. % alumina, wt. % silica, 40 wt. % calcium oxide and 20 wt. of magnesium oxide, giving a desired ratio of alumina to silica of 1.5. The combined proportion of aluminum and silicon which was used to add the heating materials both from the desired thermal regime (heating the metal bath at the above-mentioned temperature) and to achieve the above-mentioned chemical composition of the slag mentioned above was calculated according to the invention. the desired temperature rise of the metal bath of 111 ° C was determined, with an H value of 111 times 12.7 tonnes, which is 1410.

At the expected masses of alumina and silica formed in the transported metal and slag and from the reduction reactions for the AP ^ and SP ^ values, the corresponding additive to the metal melt can be detected as heating components having the following composition: 33.6 kilograms of aluminum and 9, 1 kilogram of silicon, yielding 63.0 kilograms of alumina and 19.1 kilograms of silica in slag. The total content of alumina and silica in the slag, as a result of all operations of the process of the invention, was 71.7 kilograms of alumina and 47.6 kilograms of silica to achieve the desired alumina-silica ratio of 1.5. the calcium oxide and magnesium oxide additives were 96.6 kilograms of calcium oxide and 50.3 kilograms of magnesium oxide, representing 298 kilograms of slag of a preselected chemical composition.

Claims (3)

SUBJECT OF THE INVENTION A method of controlling the composition of a metal bath slag in a converter provided with a refractory lining, preferably a magnesium chromite lining, in a process for refining the metal bath by introducing oxygen gas into the bath during the oxidation period and introducing non-oxidizing gases during the reduction period melt in such a way that the slag, after completion of the refining process, has a composition corresponding to a substantially predetermined amount of A% by weight. % Al ₂ O ₂ , B wt. silicon dioxide SiO _2, C, wt.% % CaO and D wt. MgO, wherein the ratio of alumina to silica X corresponds to a predetermined A / B value in the range of about 0.1 to about 10, characterized in that in the first step aluminum and silicon are added to the bath as a heating component in the combined from 0 to 100 wt. the aluminum and the remainder are silicon to raise the bath temperature to a predetermined level upon completion of the oxidation period, achieving an A / B ratio of alumina to silica, adjusting the weight of the alumina and silica present in the slag in the second stage after completion of the first stage, according to the stoichiometric ratio between aluminum and alumina and between silicon and silica and the weight of aluminum, alumina, silicon and silica present before the first stage, aluminum is added to the bath in the third stage, and silicon as a reducing component at any point in time after the oxidation period has been completed, with complete reduction of the metal bath, Silicon is added to the bath in the fourth stage, either concurrently with or after the third stage, to achieve the desired melt state at the time of completion of the refining process, in the fifth stage ee adjusting the alumina masses, and the silicon dioxide contained in the slag at the end of the refining process according to their relative isometric relationship 8 with aluminum and silicon and the weights of alumina and silica present prior to the third stage, and in the sixth stage calcium and magnesium oxide are added to this bath. to meet the following equations: C cao -. C and ap ₄ + sp ₄ J - cp A + B D MgO O -. £ AP ₄ + SP ₄ J-MP A + B in which AP _{4 represents the} weight of alumina in the fifth stage, SP ₄ is the mass of silica in fifth stage, CP and MP are the masses of calcium oxide and magnesium oxide already contained in the slag, Cao and MgO are corresponding to the masses of calcium oxide and magnesium oxide added in this sixth step, and A, B, C and D are predetermined percentages of said components. 2. The method of claim 1, wherein the weight of aluminum and silicon in the first stage is determined by calculating the desired weight of alumina to be formed from the aluminum as a heating component according to a smaller value obtained from the following equations: H X. - + SP ₂ J - AP ₁ ^K 1 AF = —---, ^K2 1 + _. X H AF = in which AF is the mass of alumina obtained in the first stage from the addition of aluminum as a heating component, AP ^ is the weight of alumina present in the slag at the start of the feed of the heating components, SP ^ is the mass of silica present in the slag at the start of the feed of the heating components, H is the value that corresponds to the temperature increase multiplied by the effective mass of the metal bath and the heat-resistant materials involved in thermal equilibrium, is the calculated constant representing the degrees of heat per unit mass of silica formed per unit mass of the thermal equilibrium components. Si / solid, 21 ° CJ + 0 ₂ £ gas, 21 ° C £ SiO ₂ / slag, bath temperature J, K ₂ is the calculated constant representing heat, in degrees per unit mass of alumina, formed per unit mass of the components involved in thermal equilibrium according to the following equation: 2 Al f solid, 21 ⁰ CJ + 3/2 O ₂ gas, 21 ° CJ » The temperature of the baths J7 and X is the A / B ratio, then the need for aluminum as the heating component is calculated from the stoichiometric conversion from the AF value, the desired silica mass obtained by adding silicon as the heating component is calculated according to the following equation: H - K ₂ . AF SF = ^K 1 in which SF is the mass of silica obtained from silicon as the heating component, and finally the silicon requirement as the heating component is calculated from the stoichiometric conversion of the value for SF. 3. The method of claim 2, wherein for a value of Η that is the product of the desired bath temperature increase in degrees Celsius and the weight of the temperature system in tonnes, all other masses being in kilograms, the value is 15.6 and K ₂ is 17.6.