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Mechanism of free sulfur influence on the eutectic cell count and transition from graphite to cementite eutectic in cast iron Part I. Theoretical background

Fraś E., Górny M.

Archives of Foundry Engineering

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2010

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Vol. 10, iss. 1 spec.

53--56

EN

In this work an analytical solution of general validity is used to explain the mechanism of free sulfur influence on the cell count and on the transition from graphite to cementite eutectic in cast iron. It is found that this transition can be related to the nucleation potential of graphite (represented by eutectic cell count Nv), the growth rate coefficient of graphite eutectic cell, μ the temperature range, ΔTsc and the pre-eutectic austenite volume fraction, fγ.

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Mechanism of free sulfur influence on the eutectic cell count and transition from graphite to cementite eutectic in cast iron. Part II. Experimental verification

Fraś E., Górny M.

Archives of Foundry Engineering

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2010

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Vol. 10, iss. 1 spec.

57--62

EN

In this work the mechanism of free sulfur influence on the transition from graphite to cementite eutectic in cast iron is experimentally verified. It has been shown that the main impact of free sulfur on the transition from graphite to cementite eutectic consist in reducing the growth rate of graphite eutectic cell.

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Mechanism of the silicon influence on absolute chilling tendency and chill of cast iron

Fraś E., Górny M., Lopez H. F.

Archives of Metallurgy and Materials

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2009

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Vol. 54, iss. 1

103-110

EN

In this work an analytical solution of general validity is used to explain mechanism of the silicon influence on the absolute chilling tendency (CT) and chill (w) of cast iron. It is found that CT can be related to nucleation potential of graphite (Nv), growth parameter (μ) of eutectic cells, temperature range (ΔTsc), where ΔTsc = Ts - Tc (Ts is graphite eutectic equilibrium temperature and Tc is cementite eutectic formation temperature) and the pre-eutectic austenite volume fraction (fϒ). It has been shown that silicon addition: 1) impedes the growth of graphite eutectic cells through decreasing the graphite eutectic growth coefficient (μ), 2) expands the temperature range (ΔTsc), 3) increases the nucleation potential of graphite (Nv), 4) lowers the pre-eutectic austenite volume fraction, (fϒ). In a consequence, the absolute chilling tendency (CT) decreases. The minimum wall thicknesses for chilled castings, or chill width (w) in wedge shaped castings is related to CT and as Si content increases, the chill width, w value decreases.

PL

W pracy przedstawiono wyniki rozwiązania analitycznego mechanizmu wpływu krzemu na bezwzględną skłonność żeliwa do zabieleń (CT) i zabielenia (w) w żeliwie. Wykazano, że CT jest uzależnione od potencjału zarodkowania grafitu (Nv), parametru wzrostu (μ) ziaren eutektycznych, zakresu temperatury (ΔTsc), gdzie ΔTsc = Ts - Tc (Ts jest równowagowa temperatura krystalizacji eutektyki grafitowej, a Tc jest temperatura tworzenia eutektyki cementowej) oraz udział przedeutektycznego austenitu (fϒ). Z przedstawionych badan wynika, ze dodatek krzemu: 1) utrudnia wzrost ziaren eutektycznych poprzez zmniejszenie współczynnika wzrostu eutektyki grafitowej (μ), 2) rozszerza zakres temperatury (ΔTsc), 3) zwieksza potencjał zarodkowania grafitu (Nv, 4) zmniejsza udział przedeutektycznego austenitu (fϒ) a w konsekwencji zmniejsza bezwzgledną skłonność żeliwa do zabieleń (CT). Wykazano ponadto, że minimalna grubość ścianki, powyżej której w odlewie występują zabielenia lub szerokość zabielenia klina (w) w odlewie o kształcie klina zależy od CT oraz zwiększenie zawartości krzemu prowadzi do zmniejszenia szerokości zabielania klina.

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Mechanism of silicon influence on chills in ductile iron

Górny M.

Archives of Foundry Engineering

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2009

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Vol. 9, iss. 1

147-150

EN

In the present work an analytical expression that combines the susceptibility of liquid cast iron to solidify according to the Fe-C-X metastable system (also known as the chilling tendency of cast iron, CT) is proposed. A relationship between CT and several factors has been developed. In particular the CT is related to the critical wall thickness (Scr), below which the chill is formed. Theoretical calculations of Scr were made and then compared with experimental outcome for ductile iron melts. The predictions of the theoretical analysis are in rather good agreement with the experimental data.The results can be used as a guide for a better understanding of the effect of technological variables such as the melt chemistry, the holding time and temperature, the spheroidizing and inoculation practice, the resulting nodule count and the type of mold material and pouring temperature, on the resultant chill of the ductile iron.

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Fading of inoculation effects in ductile iron

Fraś E., Górny M.

Archives of Foundry Engineering

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2008

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Vol. 8, iss. 1 spec.

83--88

EN

In work it has been shown results of investigations of influence of time lapsed form inoculation process on graphite nucleation potential represented by: number of graphite nodules N and Nv maximum undercooling ΔTm, during solidification of graphite eutectic, absolute chilling tendency CT and critical casting diameter dkr, under which cementite eutectic occur (so-called chills). Moreover it has been estimated rate of change of N and Nv, ΔTm, CT and dkr. Also, it has been proved that after one minute since the moment of inoculation process about 35% of graphite nucleation potential is lost, by 40% chilling tendency, by 70% increases maximum undercooling for graphite eutectic and by nearly 40% casting diameter has to be increased in order to avoid chills.