Use of high intensity X-ray analysis as tool to create new, fundamental models for phase transformations and residual stress in ductile cast iron

Cast irons have been used for engineering purposes for thousands of years, and still, today they are essential our society. Their mechanical properties are primarily determined by the shape, size and distribution of graphite in the steel matrix. [1] The mechanisms behind graphite growth and development of shape and their coupling to raw material quality and process conditions remain unknown.[2] Also the mechanisms leading to the formation of residual stresses are also not fully clear.[3;4] Extensive experimental data has been produced and utilized to generate empirical correlations via statistical methods, showing that e.g. the shape and distribution of graphite affect ductility, yield strength and fatigue properties while carbides influence strength and wear properties.[1] However, little is known on why such correlations hold true, as the individual mechanisms which control the material behavior at the micro-scale have not been clarified.

Recent advances in high resolution X-Ray methods that involve use of synchrotron facilities have made it possible to do high resolution, in-situ experimental studies of phase transformations in engineering materials thus providing detailed and accurate information on the processes that take place during such phase transformations.[5;6] This paper describes how such facilities can be applied to study solidification of cast iron and formation of residual stress after eutectoid transformation by resolving the processes in 3D and time.