Solid State Transformation Kinetics of high nodule count Ductile Iron

J. M. MASSONE; R.E.BOERI ; J.A.SIKORA

INTERNATIONAL JOURNAL OF CAST METALS RESEARCH

MANEY PUBLISHING

Año: 2003 vol. 16 p. 179 - 184

1364-0461

This work focuses on the study of the kinetics of  solid state transformations of thin wall ductile iron. The aim is to identify the effect of the nodule count and the matrix homogeneity on the rate of transformation. The study is carried out on samples taken from sand cast plates of thickness ranging from 1.5 to 4mm, which show nodule counts up to 1700 per square millimetre. The results are compared to those obtained on samples taken from 12.5 mm thick Y-blocks, having approximately 300 nodules per square millimetre. Kinetics of ferritising, austenitising, austempering and cementite dissolution are studied. The results show that solid state transformations involving carbon transport from the matrix to the nodules or vice versa, such as subcritical ferritising and austenitising, show  faster kinetics as the nodule count increases. The kinetics of the austempering transformation, which does not involve changes in the carbon content of the matrix, is not affected by the nodule count. The dissolution of the cementite present in unalloyed TWDI, also takes place at a very fast rate, ranging between 3 and 5 % per minute.