ISSUE 1/2013

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Fraś, E.; Górny, M. Mechanism of phosphorous influence on the chilling tendency and chill of cast iron

In this work an analytical solution is used to explain the mechanism of phosphorous 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, DTsc = Ts - Tc (where Ts and Tc are 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 chilling tendency, CT and in consequence the chill, w of cast iron. This theory is experimentally verified using phosphorous as an example. Influence of phosphorous on estimation of Ns, b and m values is presented. It has been shown that increasing phosphorous leads to increasing the critical cooling rate, Qcr. In consequence as content of phosphorous decreases the chilling tendency, CT and the width of chill, w increase. The main impact of phosphorous on the chilling tendency and chill is related with increasing the graphite nucleation potential of cast iron.

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