Mechanism of the Silicon Influence on Chilling Tendency Index and Chill of Ductile Iron in Thin Wall Castings

E. FRÁS; J. SIKORA; M. GÓRNY

International Foundry Research

World Foundrymen Org.

Lugar: Düsseldorf - Germany; Año: 2010 vol. 62 p. 2 - 8

0046-5933

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 presented. Theory was experimentally verified using silicon as an example. In particular, it has been shown that as a result of increasing silicon content the nucleation potential of graphite increases, (nodule count Ncr)  as well as the temperature range, ∆Tsc. Such variations lead decreasing the chilling tendency (CT) and in consequence reducing chills in cast iron. The chilling tendency (CT) has been 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 results can be also 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.