A new advance was made recently in electric steelmaking practice in connnection with the use of liquid pig iron as

a substitute for scrap [1–3]. The interest being shown in the use of liquid pig iron as a scrap substitute stems from the fol-

lowing considerations:

• the increase in the volume of unused pig iron and the lack of scrap metal;

• a reduction in the duration of the heat due to use of the sensible and chemical heat of the pig iron, the activation

of oxidation-reduction reactions, and the fact that the pig can be poured into the furnace while the current is on;

• conservation of electric power;

• a reduction in the amounts of natural gas and fuel that must be supplied to the furnace;

• a decrease in electrode consumption in connection with the the shortening of the heat and the decrease in the inci-

dence of electrode breakage due to the use of oversized scrap;

• a decrease in coke consumption;

• a reduction in the costs incurred in preparing and cutting the scrap metal;

• the increase in the concentrations of non-ferrous-metal impurities (chromium, nickel, copper, lead, molybdenum,

tin, etc.) in scrap metal, which sometimes makes it difficult to produce steel with the necessary chemical composition;

• a reduction in the nitrogen content of steel, due to intensification of the oxidizing period and shortening of the heat;

• shortening of the cold-charging operation (compared to the use of a charge consisting entirely of scrap – especial-

ly oversized pieces) when molten pig is added by one of the progressive new technologies [3];

• a reduction in the consumption of refractories, since the thermal loads are smaller and the lining is not mechani-

cally damaged by the charging of heavy scrap metal;

• the improvement in the quality of the steel due to the decrease in the number of exogenous nonmetallic inclusions.

However, the use of molten pig iron in the charge also has several technical and economic disadvantages:

• the greater possibility of accidents if proper procedures are not followed in adding the molten pig to the furnace;

• the need for additional capital investment in the reconstruction of the shop and the furnaces;

• an increase in slag volume (due to the high silicon content of the pig iron) and the associated costs of recycling the

slag;

• an increase in the consumption of lime to achieve the necessary slag basicity, and an increase in the amount of heat

lost with the slag;

• an increase in the consumption of manganese alloys, since the manganese content of pig iron is lower than that of

scrap metal;

• erosion of the furnace lining due to its interaction with the pig iron as it is poured into the furnace;

Metallurgist, Vol. 44, Nos. 11–12, 2000

ECONOMIC ASPECTS OF THE USE OF LIQUID

PIG IRON IN ELECTRIC STEELMAKING

SCIENCE, TECHNOLOGY, INDUSTRY

A. I. Katunin, N. A. Kozyrev,M. V. Obsharov, N. N. Timmerman,and P. E. Sychev

UDC 669.187.012.7

Open Joint-Stock Company Kuznetsk Metallurgical Combine. Translated from Metallurg, No. 11, pp. 38–39,

November, 2000.

0026-0894/00/1112-0560$25.00 ©2000 Plenum Publishing Corporation560

• an increase in the oxidation loss of ferroalloys used for deoxidation of the steel,due to the high expansion ratio

and high degree of oxidation of the slag;

• the formation of graphite flakes with a decrease in the temperature of the pig iron,which disrupts the operation of

the electrical equipment;

• the high cost of molten pig iron compared to scrap metal;

• an increase in the consumption of solid and gaseous oxidants to remove carbon from the melt.

When steel began to be made in 100-ton arc furnaces with the use of molten pig iron [4, 5], an analysis was per-

formed to determine the cost-effectiveness of that technology (with the weight of the molten pig being as much as 40% of

the total weight of the cold charge) versus the production of steel on an all-scrap charge.

It was established that when molten pig iron is used, the contribution of the cost of the metal charge to the produc-

tion cost of electric steel increases from 38.68% to 45.99%,while the corresponding contribution of the ferroalloys’ cost

increases from 7.26 to 8.03%. There is a reduction in the cost of electric power, natural gas,electrodes,oxygen,coke, and

magnesite and a moderate increase in the cost of ore and sinter.

Other conditions being equal,the production cost of steel is determined by the existing prices for liquid pig iron and

scrap metal. Here, it should be kept in mind that scrap metal is 1.9–2.2 times cheaper than liquid pig iron. However, the cost

of scrap is trending upward compared to the cost of liquid pig. Scrap costs went up 38.58% in the first half of 2000 (com-

pared to a 9.1% increase for the cost of liquid pig iron).

The use of molten pig iron reduces the unit consumption of metallic charge materials (pig iron and scrap) from

1134.3 to 1115.7 kg/ton,which is related to the impurity content of the scrap.

561

Fig. 1. Structure of the cost of electric-furnace steel when the charge contains solid pig iron (a)

and liquid pig iron (b).

Electric power 8.78%

Natural gas 0.32%

Electrodes 16.63%

Oxygen 0.80%

Magnesite 0.89%

Ore 0.56%

Sinter 0.20%

Coke 0.06%

Lime 0.65%

Scrap metal 33%

Other 25.18%

Solid pig iron 5.68%

Ferroalloys 7.26%

Electric power 3.83%

Natural gas 0.27%

Electrodes 10.95%

Oxygen 0.61%

Magnesite 0.85%

Ore 0.06%

Sinter 0.67%

Coke 0.10%

Lime 0.96%

Scrap metal 27.52%

Other 27.69%

Liquid pig iron 18.47%

Ferroalloys 8.03%

a

b

We should make special mention of the role of silicon in the use of molten pig iron. On the one hand, an increase

in the concentration of silicon increases the expansion ratio of the slag because more lime is added to maintain the appropri-

ate slag basicity. The increase in silicon content also increases the amount of heat lost with the slag. On the other hand, due

to the exothermic oxidation reactions that take place, silicon increases the heat content of the steel which is being made.

A calculation shows that when 25–30% of the weight of the metal charge consists of molten pig iron, the theoreti-

cal expansion ratio that the slag must have in order to maintain a basicity of 2.1–2.3 is 0.03–0.032 at an Si concentration of

0.4%,0.033–0.035 at an Si concentration of 0.6%,0.037–0.038 at an Si concentration of 0.8%,and 0.040–0.045 at an Si con-

centration of 1%. This makes it more difficult to evacuate the slag from the furnace. Thus,it is recommended that only pig

iron with a silicon up to 0.60% be used.

The use of liquid pig iron makes it possible to improve the quality of steel:it reduces the concentrations of chromi-

um,nickel, copper, sulfur, and nitrogen; it alleviates contamination of the steel by nonmetallic inclusions,which significantly

expands the possibilities for producing quality steels. However, failure to observe prescribed operating procedures when

pouring the hot metal into the furnace results in rapid erosion of the lining and contaminates the steel with exogenous non-

metallic inclusions. In connection with this,the shop has devised a thermal regime that prevents overheating of the high-car-

bon melt in the furnace.

When conventional charging has been employed, the amount of downtime seen in the shop due to the lack of suffi-

cient scrap metal and the poor quality of the available scrap has increased considerably (during some periods,it has increased

to as much as 26.56% of calendar time),while inadequate preparation of the metal charge has led to frequent breakages of

the electrodes. The use of liquid pig iron in the charge has made it possible to shorten the heats by 10–12 min and reduce

the consumption of electric power by 50–100 kWh/ton steel,reduce electrode consumption by 0.17–0.20 kg/ton steel,lower

coke consumption by a factor of 3–3.5,decrease the consumption of natural gas by 9.1 m3/ton, reduce the consumption of

gaseous oxygen by 0.8 m3/ton,and reduce the consumption of magnesite by 0.7 kg/ton.

REFERENCES

1. V. G. Milyuts,A. F. Bocharnikov, V. V. Kulikov, et al.,“Development of a technology for making steel in 100-ton

arc furnaces with the use of liquid pig iron,” Stal’, No. 8,30–32 (1997).

2. Yu. V. Lipukhin, O. E. Molchanov, and B. Ya. Baldaev, “Making steel in 100-ton arc furnaces with liquid pig iron

in the charge,” ibid., No. 7,26–27 (1997).

3. V. Burgman,V. Lure’e, and G. Rot, “Technology for charging modern electric arc furnaces,” ibid., No. 4, 19–23

(1999).

4. A. I. Katunin, L. A. Godik, N. S. Anashkin,et al.,“Development of a technology for making steel in electric fur-

naces with the use of liquid pig iron,” ibid., No. 5,33–35 (2000).

5. A. I. Katunin,L. A. Godik,M. V. Obsharov, et al.,“Use of liquid pig iron in electric arc furnaces,” Metallurg, No. 6,

32 (2000).

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