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ISSN 0036-0295, Russian Metallurgy (Metally), Vol. 2009, No. 8, pp. 683–687. © Pleiades Publishing, Ltd., 2009.Original Russian Text © A.E. Semin, N.A. Shevtsov, 2009, published in Elektrometallurgiya, 2009, No. 1, pp. 2–8.

Beginning from the 1990s, the number of new arcsteel-melting furnaces in metallurgical works that workwith liquid iron in a charge was constantly increasing[1–15]. This increase can be caused by various factorsinherent of every enterprise. Nevertheless, the follow-ing principal factors can be noted: an increase in thesteel quality, a decrease in the cost of steel, intensifica-tion of a heat, and organization factors.

Increase in the Steel Quality

One of the tendencies in the world steel market isthe growth of the high-quality special steel market. Asa result, metallurgists tend to increase the output ofsuch steels. To provide the competitive ability of elec-tric furnace steel, it is important to decrease the contentof impurity elements, such as Cu, Sn, Cr, and Ni. As isknown, it is very difficult to remove impurity elements.Therefore, they accumulate constantly in a metal andhinder its reuse. In practice, this problem is compli-cated by the fact that enterprises do not devote properattention to the preparation of scrap, in particular, todividing it into carbon scrap and alloyed scrap. More-over, the rate of accumulation of impurities in scrap canbe rather high in the absence of efforts made to sort thescrap. If we do not take into account organization prob-lems, the only solution at this stage is to dilute scrapwith a high content of impurities by a “pure” charge,namely, to use high-quality “pure” scrap or originalcharge, i.e., cold pig iron, metallized pellets, briquettes,Synticom, or liquid iron. Among these materials, liquidiron is distinguished, since it contains both physicalheat and a latent heat of chemical reactions. Moreover,the nitrogen content in steel decreases because of anintense decarburization reaction.

Decrease in the Cost of Steel

Since liquid iron contains physical heat and a latentheat of chemical reactions, electric power is saved, thenatural-gas and fuel flow rates decrease, the consump-tion of electrodes and coke decreases, the costs of scrappreparation and cropping decrease, and the consump-tion of refractories decreases due to a decrease in theheat loads and mechanical damages to a lining duringcharging of a heavy metallic charge.

The cost of steel can also be decreased as a result ofa decrease in the consumption of slag-forming ele-ments. However, if scrap has a high content of elementsdecreasing the activity coefficients of phosphorus andsulfur, the refining of a metal from these impuritiesbecomes difficult. Under conditions of stringentrequirements for the steel quality, this problem can besolved by increasing the multiplicity of slag, the use ofmore expensive desulfurizers, and so on. This problembecomes more and more important, since the scrapquality decreases, as follows from the forecasts of allresearchers.

The authors of [16] performed thermodynamic andbalance calculations and revealed the effect of anincrease in the copper, chromium, or molybdenum con-tent in a charge on the main parameters of metaldephosphorizaiton and desulfurization. As a result of thecalculations performed with allowance for the first-orderinteraction parameters in iron at 1600

°

C, they found thatthe coefficient of phosphorus distribution between slagand metal decreases by 7–10% at 0.04% P in a metalwhen the chromium concentration increases from 0.2 to0.5%, the nickel or molybdenum content increasesfrom 0.2 to 0.4% and the copper content increases from0.1 to 0.3%. Therefore, the dephosphorizaiton of themetal is improved when liquid iron is used, which leadsto a lower total content of impurity elements (Cu, Sn,Cr, Ni). In practice, this results in a decrease in the limeconsumption, which, in turn, makes it possible todecrease the amount of slag and, hence, to improvesome other parameters.

Solution of Various Organization Problems

Significant volumes of unclaimed cast iron appearperiodically in metallurgical works against the back-ground of faults in the supply of scrap. The situation ofblast furnaces at a long distance from a steelmakingplant is also a source of a number of technical and eco-logical problems.

Intensification of a Heat

A high arc steel-melting furnace (ASF) capacity anda decrease in the charging time and the heat time can beachieved as a result of using the physical and chemicalheat of cast iron, the activation of redox reactions, and

Use of Liquid Iron for Making Electric Furnace Steel

A. E. Semin and N. A. Shevtsov

State Technological University MISiS, Moscow, Russia

DOI:

10.1134/S0036029509080023

MANUFACTURE OF FERROUS AND NONFERROUS METALS

684

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SEMIN, SHEVTSOV

the possibility of pouring of liquid iron under an elec-tric current.

Fraction of liquid iron in a metallic charge of afurnace.

Although the problems of development ofmaking electric furnace steel using liquid iron haveattracted particular attention, there is still no generallyaccepted opinion about the optimum mass fraction ofliquid iron in the charge of a furnace. For example,according to [1, 9], electric arc furnaces operate effec-tively when liquid iron accounts for about 30% of thecharge, while, according to [7, 15], this fraction is 40%.

Table 1 gives data for some enterprises that deter-mined the optimum fraction of liquid iron in a metalliccharge (which changes from 25 to 40%) during studiesof the application of liquid iron in ASFs. As the criteriaof optimality, they used the specific electric power con-sumption, the heat time, the stability of furnace opera-tion, and so on.

For example, POSCO (Korea) found that the opti-mum quantity of liquid iron poured into an ASF during

operation is 40% of the metallic-charge mass, since thisfraction ensures a minimum heat cycle [15]. Moreover,they found that, as the fraction of liquid iron increases,the content of nitrogen and random elements decreases,the sulfur concentration increases, and the phosphoruscontent remains almost unchanged.

Figure 1 shows the basic parameters of the typicalheat using liquid iron in one of the POSCO enterprises.The steelmaking time is seen to decrease as the fractionof liquid iron increases to 40%. It was shown that theuse of 1% liquid iron in a charge saves 4.3 kWh/t. Theheat campaign is shown in Fig. 2. At 40% liquid iron,the average heat cycle is about 52 min, which is 10 minshorter than that for the operation with only scrap.However, as the fraction of liquid iron increases further,the heat cycle time increases, which is related to thenecessity of longer decarburization of a metal pool. Anincrease in the oxygen supply intensity to decrease thedecarburization time is restricted by the ASF bathdesign and can result in additional metal losses becauseof both metal splashing and effluent gases containing ahigh dust content.

The dependence of the electric melting time of theliquid iron consumption (Fig. 3) obtained in [10, 13] issimilar to that in Fig. 1. According to those works, thepresence of liquid iron in a charge decreases the meltingcycle by 8–10 min, and the optimum fraction of liquidiron is 30%. The authors of [11] performed a balance cal-culation in one of the Russian metallurgical works andpresented the parameters of ASF operation with 40% liq-uid iron in a charge. They showed that the melting timedecreases significantly and that the use of 1% liquid ironsaves 4.5 kWh electric power per 1 t steel.

Methods of pouring of liquid iron in a furnace.

Toadapt an ASF to the use of liquid iron, its design shouldprovide convenient pouring of liquid iron. The follow-ing well-known technical versions of pouring of liquidiron can be noted:

(i) Pouring of liquid iron followed by loading of acharge can increase the degree of using the pool volumeand the furnace capacity [1], since an electric furnaceoperates with complete heat tapping.

Table 1.

Electric furnace operation indices during steelmaking with liquid iron in a metallic charge for various metallurgicalenterprises

Index

Wheeling-Pittsburg

Steel Corp. (USA) [10]

OAO Mechel

[2]

OAO Severstal [2, 12]

Huta Cze-stochowa, (Poland)

[1]

OAO NKMK[3–6]

OAO Ural’skaya Stal’ [8]

POSCO, (Korea)

[15]

OAO MMK [9]

Fraction of liquid iron, % 40 25–35 25–40 30–40 30–35 20–40 40 25–30

Specific consumption:

oxygen, m

3

/t 35 40–45 46 40 – – – –

natural gas, m

3

/t (carbon, kg/t) (15) 7–10 15 4.5

electric power, kWh/t 225 300–350 280 210–220 270–290

electrodes, kg/t 1.3 2.5–3 1.15–1.25

100

20 40 600

200

300

400

500

600

70

60

50

40

30

20

w

, kW

h/t

τ

, min

q

0 2

, m

3

/t

80

80 100%

τ

q

02

w

Fig. 1.

Effect of the liquid iron content (up to 80%) on theASF operation indices:

w

is the specific electric power con-sumption,

τ

is the heat time, and is the specific oxygen

flow rate.

qO2

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USE OF LIQUID IRON FOR MAKING ELECTRIC FURNACE STEEL 685

(ii) Portion-by-portion pouring from above after thecentral part of a metallic charge is melted and a liquidmetal pool forms. Although the technology makes itpossible to rapidly pour entire liquid iron [5, 9, 12, 15],the furnace bottom lining becomes worn. In the case ofan intense reaction, even water-cooled panels becomeworn [1].

(iii) Pouring of liquid iron through a charging holeby a portable chute requires an additional crane time.This technology cannot be used at the early stages of aheat, since the charging hole should be free of scrap andpure. Otherwise, liquid iron solidifies during contactwith a cold charge, which will cause the reverse motionof liquid iron after the hole is closed by a metal. There-fore, some metallurgical works refuse this technology(ISCOR, POSCO) [7].

(iv) Pouring of liquid iron during the operation of afurnace using a stationary lateral chute mounted in anASF jacket [7]. Liquid iron is supplied from a ladleplaced on a stationary tippler or a tiltable hot-metalladle. Although this version of pouring can cause somedifficulties [9], it can decrease the heat cycle time by 3–4 min for an adjusted technology.

According to the data of studying the first two ver-sions of pouring liquid iron and their modifications, thefirst version does not yield significant profit and,according to [5], is unacceptable. For example, whenscrap is charged onto liquid iron poured into a furnace,the specific electric power consumption increases dueto the fact that liquid iron solidifies in the furnace alongwith scrap and forms a cast iron–steel conglomeratethat is difficult to melt. The second version of pouringliquid iron is preferred; however, it is performed aftermelting of main and additional charges, since thecharge is not ready. However, this is related to high heatlosses. The first version is thought to cause a number ofadditional difficulties associated with the operation of

an electric furnace with complete heat tapping. Forexample, problems of cutting a furnace slag during heattapping should appear, and large temperature dropstake place, which degrades the resistance of the furnacebottom lining. For a heat with a retained metal and slag,the formation time of a new slag decreases, whichincreases the refining possibilities due to an increase inthe solubility of lime. However, this version is also peri-odically used for operation during hot repairing of thefurnace lining.

Additional required equipment.

An electric fur-nace operating with liquid iron can achieve a highcapacity at a high heating rate and decarburization of amelt and timely removal of slag. Therefore, an electricfurnace operating with liquid iron should have addi-

W, dolomite 0.5 t

100 kA

Consumed energy

τ

, min

Stages 1st Additional 2nd melting Refining Tapping and

Burners

Oxygen

4000–6000 m

3

/h

Foaming material: 60, 100 kg/min

720 V

CaO 2 tdolomite 0.5 t

550 V650V

100 kA

MWh

charging preparation

and foaming

material

CaO 2 t

80 kA500V 550V

90 kA

melting

40

30

20

10

0 5 10 15 20 25 30 35 40 45 50 55

8000 m

3

/h10000 m

3

/h

7000 m

3

/h

Fig. 2.

Process of steelmaking in an ASF using liquid iron [15].

10 20 30 40 500100

200

300

4050

60

80

100

120

w

, kW

h/t

τ

, min

G

, t/h

Fraction of liquid iron, %

Fig. 3.

ASF operation indices when liquid iron is used [13]:

G

is the furnace capacity,

τ

is the heat time from tapping totapping, and

w

is the specific electric power consumption.

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SEMIN, SHEVTSOV

tional equipment (Table 2). As a rule, this equipment isnot excessive: it is required for any conventional fur-nace rather than for heats with liquid iron.

According to the data of various authors [1–15], theresults of operation of an ASF with liquid iron in acharge cover the costs required for this scheme andmake it possible to significantly improve the steelmak-ing indices.

Apart from advantages, the use of liquid iron alsohas disadvantages.

One of the main technological problems is the pos-sibility of emergency situations related to nonregulatedconditions of pouring liquid iron into a furnace and dif-ferent degrees of oxidation of mixed melts. The degreeof oxidation of a metal is known to be controlled by thecarbon content in it; therefore, the difference in oxygencontents in scrap and cast iron melts is significant.

We estimated the difference in the degrees of oxida-tion of scrap and cast iron melts. As a rule, the elementcontents upon melting of scrap is as follows (wt %):0.2–0.4 [C], 0.05–0.1 [Si], 0.1–0.2 [Mn], 0.03–0.04 [P],0.03–0.05 [S], ~0.2 [Cu], ~0.2 [Cr], and ~0.2 [Ni].

The carbon content in cast iron was taken to be 4%.As follows from practice, the oxygen content in the

first melt falls in the range between the values in equilib-rium with carbon and iron oxides in slag. We acceptedthe following slag composition in a furnace (wt %):~25 (FeO), ~10 (MnO), ~35 (CaO), ~10 (MgO), and~20 (SiO

2

).The oxygen concentration in cast iron is determined

by the fraction of carbon in it.If the first melt has a temperature of 1600

°

C and liq-uid iron has a temperature of 1350

°

C, the metal basedon a scrap melt contains at least 0.04% oxygen and theoxygen content in liquid iron is 0.015%. An almostthreefold difference in the degrees of oxidation of thesetwo melts cannot but affect the character of interactionbetween these two melts, namely, the decarburizationintensity. The difference in the degrees of oxidation ofthese two melts begins to manifest itself as the averagemelt temperature increases. The main danger consistsin the fact of a sharp change in the metal pool boilingintensity.

Moreover, the wear of the furnace lining canincrease when liquid iron is used because of the inter-action of the lining with poured liquid iron, and the fer-roalloy losses can increase during steel deoxidation ina furnace because of a high multiplicity and degree ofoxidation of slag. When liquid iron is poured, refiningfoam forms because of a decrease in the liquid irontemperature; this leads to breaks in the operation ofelectric equipment [5], the creation of dangerous situa-tions for a staff, and the degradation of ecological con-ditions in a plant.

By analogy with the decarburization in converters,the carbon content in steel pool during blowing doesnot affect the decarburization rate to certain criticalconcentrations, which are 0.1–0.2%. According to [18],the factor that controls the carbon oxidation rate at ahigh carbon concentration is the oxygen supply rate. Asa result, we can write

–

dC

/

d

τ

=

a

·

v

·

k

O

/

V

M

,

where

dC

/

d

τ

is the carbon oxidation rate (mol/(cm

3

min)),

a

is the coefficient of oxygen utilization,

v

is the rate ofoxygen supply to the metal (cm/min),

k

O

is the oxygencontent in the blast (mol/cm

3

), and

V

M

is the metal poolvolume (cm

3

).

Depending on the blowing intensity, the decarburiza-tion rate in a converter can change in the range 0.25–0.5%/min [19]. Such high rates cannot be achieved in anASF. For example, according to [15], decarburizationcan be considered using the equilibrium reactionbetween oxygen and carbon when liquid iron isemployed in the production of electric furnace steel. Thedecarburization rate weakly depends on a change in theblowing intensity and falls in the range 0.05–0.06%/minat a high carbon concentration. This brings up the ques-tion: How can we increase the decarburization rate in anASF when liquid iron is used? The answer to this questionwill allow us to increase the fraction of liquid iron duringthe production of electric furnace steel if necessary.

It should also be noted that the use of liquid ironrequires additional investments in restructuring plantsand furnaces, railways for supplying liquid iron from ablast-furnace to an arc-furnace plant, the production of

Table 2.

Auxiliary equipment for ASFs in various metallurgical enterprises

CompanyWheeling-Pitts-burg Steel Corp.

(USA) [10]OAO Mechel [2] OAO Severstal’

[2]Huta Czestochowa,

(Poland) [1] OAO MMK [9]

Tuyere burners, pcs (oxy-gen/natural gas flow rate, m

3

/h)

4 2(up to 3500/up to 1100)

4 1(up to 2800/up to 350)

Coal injectors, pcs(consumption, kg/min)

3 2 2(up to 100)

Gas-oxygen burners, pcs (power, MW)

6 (3.2) On hand 5 (3.5)

Oxygen tuyeres, pcs 5 1

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USE OF LIQUID IRON FOR MAKING ELECTRIC FURNACE STEEL 687

a hot-metal ladle, and so on and solving the problemsof logistics.

The main problem for the use of liquid iron is itshigh cost compared to scrap. Moreover, slag volumesincrease because of the high silicon content in liquidiron, the related costs of its utilization grow, the limeconsumed for the required basicity of slag increases,and the heat losses with slag increase. This problemcould be resolved when Romelt cast iron is used. Ascompared to blast-furnace cast iron, this cast iron hasan obvious advantage for steelmaking, namely, the sili-con and manganese concentrations in it do not exceed0.15% [17]. The authors of [17] analyzed the possibil-ity of using the Romelt process to produce a metal witha carbon content of 1–2%, which could widen the limitsof using partly refined liquid iron from 40 to 50–60%during the production of electric furnace steel.

CONCLUSIONSThus, at present and in the near future, liquid iron is

used as a charge component for the production of elec-tric furnace steel that can decrease the content of non-ferrous impurities in steel and improve a number oftechnical and economic indices.

However, the fraction of liquid iron in a metalcharge will increase only in integrated works due to thecost of liquid iron and the structure of an enterprise. Asfor miniworks, liquid iron can be of interest only if thetraditional coke–sinter–blast-furnace scheme of its pro-duction is replaced by an alternative scheme, such asthe Romelt process, which can be rather promising forthe development of ore bases with a low iron content.For example, according to the calculation data in [20],the necessity of application of liquid iron in miniworksseems to be real under certain conditions. As an example,we refer to [21], where data on the use of liquid iron inChinese miniworks are given from 2000 to 2006.

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