Ductile iron shrinkage control through graphite nucleation and growth

The present paper is undertaken with the objective of describing a new approach to treatment alloy design for improved casting performance and solidification shrinkage control. Ferrosilicon alloys for nodularizing and inoculation are developed containing balanced levels of Magnesium, Calcium, Cerium or Lanthanum that are adjusted to minimize chill and shrink formation in ductile iron. Also, specialty alloys are designed, containing Sulphur and Oxygen in a form that makes them available for reaction during introduction into liquid iron,. The new treatment alloy concept is designed to give highly powerful graphite nucleation conditions in ductile irons along with effective chill and shrinkage reduction. Manipulating the content and type of rare earth's used in alloys is found to have a pronounced impact on the cooling curve characteristics and the subsequent solidification microstructure. Nucleation and growth of graphite is focused to the end of solidification, where graphite expansion is mostly needed to counteract for shrinkage. Examples from foundry testing are reviewed, and the unique characteristics of this new alloying concept described.