ISSN 0967�0912, Steel in Translation, 2011, Vol. 41, No. 4, pp. 323–325. © Allerton Press, Inc., 2011.Original Russian Text © O.Yu. Sheshukov, E.A. Vyaznikova, V.G. Smirnova, L.A. Ovchinnikova, 2011, published in “Stal’,” 2011, No. 4, pp. 28–30.

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Alloys based on ferrosilicon are widely used in thereduction and alloying of steel, the modification ofcast iron, the production of hydrogen, the productionof heavy suspensions, and elsewhere [1]. Silicon isadded to hot metal to improve the graphitization con�ditions, the mechanical properties, and the fluidity.

In hot�metal treatment, the effectiveness and sta�bility of the process depend on the dimensions of thestructural components and the distribution of modify�ing particles within the volume. In ingots with a highsilicon content, considerable liquation of silicon isobserved over the height, as we know from our ownresearch and literature data [2]. This is associated withthe difference in density of iron and silicon, whichresults in nonuniform chemical and phase composi�tion of the resulting ingot and complicates the subse�quent modification process. This may be remedied bychanging the solidification rate of the ferroalloy andhence the dimensions and distribution of the struc�tural components [3].

Another important characteristic of the modifiersis their melting point, which determines both the rateof solution and the mechanism of this process. There�fore, effective use of ferrosilicon requires study of thealloy’s microstructure and its melting point.

In the present work we investigate samples of FS65ferrosilicon (whose chemical composition corre�sponds to State Standard GOST 1415–93) obtained inplant conditions (sample FS65) and in the laboratoryin a Tamman furnace. The laboratory samples arecooled and solidified in a quartz tube by the suctionmethod, with further cooling in water at ~800°C/min(sample FS65�1); in air in a crucible at ~130°C (con�ventional cooling; sample FS65�2); and with the fur�nace at ~12°C/min (slow cooling; sample FS65�3).

Our goal is to identify any differences in the forma�tion of the ferroalloy’s structure and phase compositionat different cooling and solidification rates. The struc�ture of the ferrosilicon samples is investigated by meansof a NEOPHOT�2 optical microscope, equipped with aSIAMS�700 computerized image�analysis system, at

(50–500)�fold magnification. X�ray structural phaseanalysis is conducted on a DRON�3.0 diffraction unit.The thermal properties of the ferrosilicon samples arestudied by means of a NETZSCH STA 449C Jupitersynchronous thermoanalyzer.

X�ray structural phase analysis shows that the fer�rosilicon samples obtained in laboratory and plantconditions have the same phase composition. Thebasic phases are silicon and iron disilicide, with smallquantities of the oxides SiO2 and Fe2O3. In Fig. 1, weshow diffraction patterns for the ferrosilicon samples.

Samples obtained at different solidification ratesdiffer in the lattice parameter a of the silicon phase andthe elementary�cell volume V, as we see in the table.

The lattice period a of pure silicon is 0.5430 nm,according to [4]. For the rapidly cooled modifierFS65�1, the air�cooled modifier FS65�2, and themodifier FS65 obtained in plant conditions, weobserve decrease in a. This may indicate solution of asmall quantity of iron in the silicon phase, with conse�quent change in its melting point.

Data on the variation in chemical composition showthat the slow�cooled sample FS65�3 is characterized by

Influence of the Cooling Rate on the Structure of Silicon FerroalloysO. Yu. Sheshukov, E. A. Vyaznikova, V. G. Smirnova, and L. A. Ovchinnikova

Institute of Metallurgy, Ural Branch, Russian Academy of Sciences, Yekaterinburg, Russia

Abstract—The influence of the cooling rate on the phase composition and the size and distribution of struc�tural components in ferrosilicon samples is investigated. The thermal properties of FeSi samples solidified atdifferent rates are determined.

DOI: 10.3103/S0967091211040206

Lattice parameters of silicon phase

Sample a, nm V, nm3

FS65�1 0.54261 0.1598

FS65�2 0.54238 0.1596

FS65�3 (top) 0.54398 0.1610

FS65�3 (middle) 0.54309 0.1602

FS65�3 (bottom) 0.54291 0.1600

FS65 0.54275 0.1599

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SHESHUKOV et al.

silicon liquation from 59.7% in the lower section to69.2% in the upper section of the ingot. The lattice vol�ume and period of the silicon phase vary over the ingotheight. For the rapidly cooled sample FS65�1, there isno liquation. The sample has a uniform chemical com�position; its silicon content is 65.8 wt %.

Analysis of metallographic data shows that the sili�con phase is deposited as needles (Fig. 2). The remain�ing surface in the section is occupied by FeSi2 phase andpores. The porosity of the rapidly cooled sampleFS65�1 is twice that of the slow�cooled sample FS65�3:11.62%, as against 6.43%. With change in solidificationrate, the particle size of the silicon phase changes. Thesilicon needles grow larger with decrease in the coolingrate. Thus, the needle thickness is ~57 µm for rapidlycooled sample FS65�1, ~80 µm for air�cooled sampleFS65�2, and ~157 µm for slow�cooled sample FS65�3.

The melting points of the phases obtained in sam�ples cooled at different rates differ somewhat (Fig. 3).Analysis of the mass change on heating indicates thatthe mass increases by 0.32% for rapidly cooled sampleFS65�1 and by 0.29% for slow�cooled sample FS65�3.The uniform mass variation may be attributed to oxi�dation of the sample surface.

Differential calorimetry shows that the heat�fluxcurves of the rapidly cooled sample FS65�1 includetwo endothermal effects: the first beginning at 1198°Cand with a peak at 1227°C, and the second with a peakat 1299°C. The basic phases in the FS65 ferrosiliconsamples are Si and FeSi2, with melting points of1300°C and 1220°C, respectively, according to [1].Hence, the thermogram may be explained by thebehavior of these phases. The peak of the endothermaleffect at 1227°C is associated with melting of FeSi2,and the peak at 1299°C with melting of Si.

The heat�flux curves of the slow�cooled sampleFS65�3 also include two endothermal effects associ�ated with the melting of crystalline silicon and irondisilicide, but they are shifted to lower temperatures:

700

600

500

400

200

100

0

300

111

111

2

34

2

2

(a)I/I0

700

600

500

400

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100

0

300

111

111

2

3 4

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2

(b)

700

600

500

400

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0

300

111

1

11

2

3 4

2

2

(c)

2θ(CuKα)

Fig. 1. Diffraction patterns of ferrosilicon samples cooledat ~800°C/min (a) and ~130°C/min (b) and samplesobtained in plant conditions (c): (1) FeSi2; (2) Si;(3) SiO2; (4) Fe2O3.

(b) (c)(а)

Fig. 2. Microstructure of ferrosilicon samples solidified at different rates: (a) in a quartz tube in water at ~800°C/min; (b) in airin a crucible at ~130°C; (c) with the furnace at ~12°C/min; ×25.

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INFLUENCE OF THE COOLING RATE ON THE STRUCTURE OF SILICON FERROALLOYS 325

the first begins at 1192°C and has a peak at 1225°C,and the second has a peak at 1255°C. The differencein melting points may be attributed to small differ�ences in chemical composition of the phases withinthese samples.

CONCLUSIONS

With change in the cooling and solidification ratesof ferrosilicon samples, the phase composition isunchanged. However, the lattice period of the siliconphase changes, and the solidification range of the fer�rosilicon samples is modified. The thickness of the sil�icon needles in the rapidly cooled sample(~800°C/min) is practically a third as large as the sili�con phase in the slow�cooled sample (~12°C/min, inthe furnace). Faster cooling yields a material that isuniform in structure and chemical composition. Thismay result in more stable chemical composition,structure, and mechanical properties of the hot metalto which the ferrosilicon is added.

ACKNOWLEDGMENTS

Financial support for this research was providedwithin the framework of the NSh�5253�2010.3project.

REFERENCES

1. Mizin, V.G., Chirkov, N.A., Ignat’ev, V.S., et al., Fer�rosplavov: spravoch. izd. (Ferroalloys: A Handbook),Moscow: Metallurgiya, 1992.

2. Shchedrovitskii, Ya.S., Vysokokremnistye ferrosplavy(High�Silica Ferroalloys), Moscow: Metallurgizdat,1961.

3. Smirnov, V.G., Vyaznikova, E.A., Ovchinnikova, L.A.,et al., Microstructure and Chemical Composition ofthe Phases in a Magnesium�Bearing Modifier Obtainedat Different Cooling Rates, Elektrometallurgiya, 2009,no. 4, pp. 33–36.

4. Gasik, M.I., Marganets (Manganese), Moscow: Metal�lurgiya, 1992.

0

–1

–2

–3

–4

–5

12001000800600400200

Temperature, °C

–6 1225.0

1256.0

1191.8

921.0

904.9

Thermal effect, mW/mg

Exothermal effect

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–61227.1

Exothermal effect 902.2

911.1

1198.1

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1307.8

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(b)

Fig. 3. Thermograms of ferrosilicon samples solidified at~800°C/min (a) and ~12°C/min (b) when heated at20°C/min in an argon current.