Mechanism of the Silicon Influence on Absolute Chilling Tendency and Chill of Cast Iron

In this work an analytical solution of general validity is used to explain mechanism of the silicon influence on the absolute chill 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 (fγ). It has been shown that silicon additions: 1) impede the growth of graphite eutectic cells through decreasing 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, fγ and in consequence the absolute chilling tendency CT decreases. The minimum wall thicknesses for chilled castings, or chill widths, w in wedge shaped castings is related to CT and as Si contents increases, the chill widths, w value decreases.