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UDC 669.18:546.621’17 INTERACTION OF THE REFRACTORY LINING OF THE HEARTH OF AN ELECTRIC ARC FURNACE WITH NONFERROUS METALS OF THE SCRAP CHARGE V. A. Kudrin, 1 A. S. Guzenkova, 1 S. S. Ivanov, 1 and G. A. Isaev 1 Translated from Ogneupory i Tekhnicheskaya Keramika, No. 4, pp. 53 – 55, April, 2003. The interaction of the refractory material of the electric furnace hearth with molten nonferrous components of the metallic mixture is studied. At elevated temperature, the nonferrous components are accumulated by infil- tration in the furnace refractory and thus may be a source of contamination. The use of scrap charges contain- ing nonferrous metal impurities constitutes a danger for electric furnaces of small capacity. The interaction between the refractory lining of steel- making plants and the metallic mixture containing materials such as galvanized iron, disused engineering components made of copper, tin, etc. regarded as a subject of investiga- tion, has a recent history. The point is that in the ever-in- creasing application of continuous steel casting technologies, the share of “pure” steel scrap (free of nonferrous metals and typically used in the charging of arc furnaces) tends to de- crease whereas that of obsolete crap, frequently high in unde- sirable nonferrous metal impurities (copper, tin, zinc, lead, arsenic, antimony, etc.) tends to increase correspondingly. This results in significant “contamination” of the commercial steel product with nonferrous metal impurities. Interactions in the refractory — nonferrous metal system constitute an is- sue of special concern in the electrometallurgy where the greater part of the metallic mixture is typically obsolete scrap, the main source of nonferrous metal impurities. The problem of removing nonferrous metals under con- ventional production conditions remains to be solved despite the fact that the presence of nonferrous impurities, even at the level of a few hundredths of a percent, can degrade ap- preciably the properties of steels, especially detrimental in the production of high-quality structural steel. The occur- rence of several impurities (for example, tin and copper) at higher concentrations is particularly undesirable. In most cases, prior to producing a relatively homoge- neous metal melt, the mixture is subjected to “warm-ups” lasting from several minutes by converter technology to se- veral hours — in blast furnaces or in low-capacity electric furnaces. During these operations, low-melting point impuri- ties (tin, lead, zinc, copper) melt and finally find their way to the hearth of the furnace. Nonferrous metals with a low melt- ing point convert to a molten state well before the steel melt- ing temperature is reached. Therefore, even if the total con- tent of nonferrous impurities in the charged mixture is low (several hundredths or even thousandths of a percent), in cer- tain periods of time (at the onset of melting), the local con- centration of the impurity melt at its contact with refractory lining may be quite high, occasionally close to 100%. This may result in an interaction between the material of the lin- ing and low-melting nonferrous metals. Our goal in this study was to see in what a manner the re- fractory lining may interact with low-melting liquid compo- nents of the mixture. The model impurities selected were me- tallic tin (for its low melting point) and metallic zinc (for its high volatility). The hot surface temperature of the furnace hearth during a warm-up period was by convention taken to be 800 – 900°C. The refractory material of the hearth was chromium magnesite with a total porosity of 16%. The test specimens cut out of the refractory material had dimensions of 30 ´ 30 ´ 12 mm. The metal chips for testing with a weight of 2 – 4 g (a VRL-200 analytical balance was used for weighing) were placed on the refractory surface and cov- ered with an Alundum crucible to prevent them from oxida- tion and volatization. The test specimens thus prepared were heated in a muffle furnace at 800 and 900°C for 15, 30, 45 and 60 min. The maximum metal — refractory contact time was 60 min, allowing for the fact that, under actual condi- tions even for low-capacity furnaces, within 60 min after the onset of melting, a pool of molten phase composed mainly of iron is formed at the furnace hearth, and the activity of non- ferrous metals under these conditions is insignificant. The test specimens heated for a specified time were put out of the Refractories and Industrial Ceramics Vol. 44, No. 4, 2003 242 1083-4877/03/4404-0242$25.00 © 2003 Plenum Publishing Corporation 1 Moscow State Night Institute of Metallurgy, Moscow, Russia.

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Page 1: Interaction of the Refractory Lining of the Hearth of an Electric Arc Furnace with Nonferrous Metals of the Scrap Charge

UDC 669.18:546.621’17

INTERACTION OF THE REFRACTORY LINING OF THE HEARTH

OF AN ELECTRIC ARC FURNACE WITH NONFERROUS METALS

OF THE SCRAP CHARGE

V. A. Kudrin,1 A. S. Guzenkova,1 S. S. Ivanov,1 and G. A. Isaev1

Translated from Ogneupory i Tekhnicheskaya Keramika, No. 4, pp. 53 – 55, April, 2003.

The interaction of the refractory material of the electric furnace hearth with molten nonferrous components of

the metallic mixture is studied. At elevated temperature, the nonferrous components are accumulated by infil-

tration in the furnace refractory and thus may be a source of contamination. The use of scrap charges contain-

ing nonferrous metal impurities constitutes a danger for electric furnaces of small capacity.

The interaction between the refractory lining of steel-

making plants and the metallic mixture containing materials

such as galvanized iron, disused engineering components

made of copper, tin, etc. regarded as a subject of investiga-

tion, has a recent history. The point is that in the ever-in-

creasing application of continuous steel casting technologies,

the share of “pure” steel scrap (free of nonferrous metals and

typically used in the charging of arc furnaces) tends to de-

crease whereas that of obsolete crap, frequently high in unde-

sirable nonferrous metal impurities (copper, tin, zinc, lead,

arsenic, antimony, etc.) tends to increase correspondingly.

This results in significant “contamination” of the commercial

steel product with nonferrous metal impurities. Interactions

in the refractory — nonferrous metal system constitute an is-

sue of special concern in the electrometallurgy where the

greater part of the metallic mixture is typically obsolete

scrap, the main source of nonferrous metal impurities.

The problem of removing nonferrous metals under con-

ventional production conditions remains to be solved despite

the fact that the presence of nonferrous impurities, even at

the level of a few hundredths of a percent, can degrade ap-

preciably the properties of steels, especially detrimental in

the production of high-quality structural steel. The occur-

rence of several impurities (for example, tin and copper) at

higher concentrations is particularly undesirable.

In most cases, prior to producing a relatively homoge-

neous metal melt, the mixture is subjected to “warm-ups”

lasting from several minutes by converter technology to se-

veral hours — in blast furnaces or in low-capacity electric

furnaces. During these operations, low-melting point impuri-

ties (tin, lead, zinc, copper) melt and finally find their way to

the hearth of the furnace. Nonferrous metals with a low melt-

ing point convert to a molten state well before the steel melt-

ing temperature is reached. Therefore, even if the total con-

tent of nonferrous impurities in the charged mixture is low

(several hundredths or even thousandths of a percent), in cer-

tain periods of time (at the onset of melting), the local con-

centration of the impurity melt at its contact with refractory

lining may be quite high, occasionally close to 100%. This

may result in an interaction between the material of the lin-

ing and low-melting nonferrous metals.

Our goal in this study was to see in what a manner the re-

fractory lining may interact with low-melting liquid compo-

nents of the mixture. The model impurities selected were me-

tallic tin (for its low melting point) and metallic zinc (for its

high volatility). The hot surface temperature of the furnace

hearth during a warm-up period was by convention taken to

be 800 – 900°C. The refractory material of the hearth was

chromium magnesite with a total porosity of 16%. The test

specimens cut out of the refractory material had dimensions

of 30 � 30 � 12 mm. The metal chips for testing with a

weight of 2 – 4 g (a VRL-200 analytical balance was used

for weighing) were placed on the refractory surface and cov-

ered with an Alundum crucible to prevent them from oxida-

tion and volatization. The test specimens thus prepared were

heated in a muffle furnace at 800 and 900°C for 15, 30, 45

and 60 min. The maximum metal — refractory contact time

was 60 min, allowing for the fact that, under actual condi-

tions even for low-capacity furnaces, within 60 min after the

onset of melting, a pool of molten phase composed mainly of

iron is formed at the furnace hearth, and the activity of non-

ferrous metals under these conditions is insignificant. The

test specimens heated for a specified time were put out of the

Refractories and Industrial Ceramics Vol. 44, No. 4, 2003

2421083-4877/03/4404-0242$25.00 © 2003 Plenum Publishing Corporation

1 Moscow State Night Institute of Metallurgy, Moscow, Russia.

Page 2: Interaction of the Refractory Lining of the Hearth of an Electric Arc Furnace with Nonferrous Metals of the Scrap Charge

furnace and allowed to cool; the remaining metal was re-

moved from the refractory surface. To determine the mass of

metal m(Me) infiltrated into the refractory, the specimens be-

fore and after heat treatment were weighed to the nearest

0.0001 g. A PRIM-1M x-ray radiometric instrument

(VNIITFA, [1]) was used to determine the amount of metal

infiltrated into the refractory material.

Relevant data are presented in Figs. 1 and 2 and in Ta-

ble 1. Figure 1 shows that the infiltration of zinc into the re-

fractory at 800°C is active within the first 15 min; later (with

the test time extended up to 60 min), the concentration of

zinc measured at the opposite face of the test specimen re-

mains virtually constant (about 2.0 wt.%). If the temperature

is raised to 900°C, the measured Zn concentration increases

to 2.7 wt.%, that is, the infiltration of zinc into the refractory

material at this temperature proceeds at a higher rate.

The infiltration of tin into the refractory (Fig. 2) likewise

increases as the test temperature is raised from 800 to 900°C.

However, the tin concentration at the specimen’s face oppo-

site to the molten-metal contact face did not exceed 1 wt.%.

The course of time curve for the concentration of infiltrated

tin measured at the opposite face resembles that for zinc: the

infiltration rate is maximum within the first 15 and 30 min.

The total mass of metal sorbed at the refractory surface in-

creases with temperature (Table 1). Assuming that the inter-

action of a fluid metal with a porous refractory materials

obeys the diffusional mass transfer in capillary systems (ca-

pillary infiltration) [2 – 9], the effective diffusion coefficient

Def was calculated from the experimental data. For both zinc

and tin, the value of Def in the temperature range 800 –

900°C is roughly of the same order of magnitude. Still, de-

spite the close values of Def , the sorption of zinc and tin dif-

fers somewhat and tends to increase with temperature.

The results obtained have important technological impli-

cations, especially for small-capacity arc furnaces. We as-

sume that the hearth of the arc furnace has the simple shape

of a truncated cone; using data from [10, 11], the specific

hearth surface per unit mass of molten metal was calculated

as a function of the furnace capacity. As an be seen from

Fig. 3, the specific hearth surface is highest for furnaces of

small capacity. Recall that electric furnaces of small capacity

are best suited for making steels with special quality requi-

rements.

CONCLUSIONS

Our data on the infiltration of zinc and tin into the refrac-

tory material show that, during the warm-up period, low-

melting components of the metallic mixture are accumulated

Interaction of the Refractory Lining with Nonferrous Metals of the Scrap Charge 243

TABLE 1. Calculated Diffusion Coefficients for Zinc

and Tin Infiltrated into the Chromium Magnesite Refrac-

tory

MetalTemperature,

°C

Infiltrated

metal mass

m (Me) � 102, g

Def � 10 – 5,

cm2�sec

Zn 800 7.1 3.46

Zn 900 8.3 3.90

Sn 800 8.7 2.77

Sn 900 9.6 2.77

3.0

2.0

1.0

15 30 45 60

2

1

Zin

cm

ass

frac

tion

(Zn),

%�

Contact time , min�

Fig. 1. Kinetics of infiltration of molten zinc into the refractory:

1 ) at 800°C; 2 ) at 900°C.

15 30 45 60

2

1

Tin

mas

sfr

acti

on

(Sn),

%�

Contact time , min�

1.0

0.8

0.6

0.4

0.2

Fig. 2. Kinetics of infiltration of molten tin into the refractory:

1 ) at 800°C; 2 ) at 900°C.

Sp

ecif

icsu

rfac

e,

10

,m

ton

Sm�

�2

2�

Furnace capacity, tons

20

15

10

50 100 150 200

Fig. 3. Specific surface per ton molten metal plotted as a function of

the furnace capacity.

Page 3: Interaction of the Refractory Lining of the Hearth of an Electric Arc Furnace with Nonferrous Metals of the Scrap Charge

in the refractory lining. This creates a danger, since in subse-

quent heats the fluid metal comes into contact with the lining

infiltrated with a certain amount of nonferrous metals. The

infiltrated lining may serve as a contaminating “donor” for

the fluid steel in subsequent heats. The use of scrap charges

containing nonferrous metal impurities may constitute a dan-

ger for electric furnaces of small capacity.

REFERENCES

1. V. P. Bovin, V. P. Varvaritsa, L. G. Savitskii, and K. I. Shchekin,

“Achievements and prospects for x-ray fluorescence analysis

instrumentation,” in: Atomic Science and Technology, Ser. Radi-

ation Engineering, Issue 3(43) [in Russian] (1990), pp. 34 – 40.

2. A. N. Tikhonov and A. A. Samarskii, Equations of Mathemati-

cal Physics [in Russian], Nauka, Moscow (1977).

3. K. K. Strelov and I. D. Kashcheev, Diffusion and Reactions in

the Solid-State Phase of Silicates and High-Melting Point Oxi-

des [in Russian], Izd. UPI, Sverdlovsk (1983).

4. G. A. Aksel’rud and M. A. Al’tshuller, An Introduction into the

Capillary Chemical Engineering [in Russian], Khimiya, Mos-

cow (1983).

5. L. I. Kheifets and A. V. Neimark, Multiphase Processes in Po-

rous Bodies [in Russian], Khimiya, Moscow (1982)

6. P. S. Mamykin, V. A. Rogozinnikov, I. L. Shchetnikova, et al.,

“Resistance of magnesia components to the attack by melted

blister copper products,” Ogneupory, No. 6, 38 – 42 (1966).

7. L. I. Kuz’min, “Wetting effect of copper and copper oxides on

refractory components,” Ogneupory, No. 12, 30 – 34 (1973).

8. P. P. Budnikov and A. M. Ginstling, Reactions in Mixtures of

Solid-State Materials [in Russian], Stroiizdat, Moscow (1971).

9. A. D. Panasyuk, V. S. Fomenko, and G. G. Glebova, Corrosive

Resistance of Nonmetallic Materials to Melts. Handbook [in

Russian], Naukova Dumka, Kiev (1986).

10. A. F. Kablukovskii, O. E. Molchanov, and M. A. Kablukov-

skaya, Electric Steelmaker’s Handbook [in Russian], Metallur-

giya, Moscow (1994).

11. V. P. Grigor’ev, Yu. M. Nechkin, A. V. Egorov, and L. E. Ni-

kol’skii, Design and Development of Equipment for Steel-

making Industry [in Russian], MISIS, Moscow (1995).

244 V. A. Kudrin et al.