ISSUE 3/2012

/// 01
Fraś, E.; Górny, M.
Mechanism of silicon influence on chilling tendency and chill of cast iron

In this work an analytical solution is used to explain mechanism of silicon influence on the transition from graphite to cementite eutectic in cast iron. It is found that this transition can be related to: (1) the nucleation potential of graphite characterized directly by the nucleation coefficients Ns and b, (2) the growth rate coefficient of graphite eutectic cell, m, (3) the temperature range, DTs,c = Ts - Tc (where Ts and Tc is the equilibrium temperature of the graphite eutectic and formation temperature of the cementite eutectic respectively) and (4) the liquid volume fraction, fl after solidification of the pre-eutectic austenite. Analytical equations were used to describe the absolute, CT and the relative chilling tendency, CTr and in consequence the chill, w of cast iron. This theory was experimentally verified using silicon as an example. Influence of silicon on estimation of Ns, b and m values was presented. It has been shown that increasing silicon leads to increasing the critical cooling rates, Qcr. In consequence as silicon content decreases the chilling tendency, CT and CTr and the width of chill, w increase. The main impact of silicon on the transition from graphite to cementite eutectic consist is related with the nucleation coefficient, Ns and the growth rate coefficient of graphite eutectic cell, m. Finally, it has been shown that the chilling tendency indexes, CT, CTr and in consequency the chill can be estimated from simple thermal analysis in referece castings. In this work, the experimental and theoretical results are found to be in good agreement with each other.




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