UNDERSTANDING CAST IRON MATERIALS AND COMPONENTS: A NEVER ENDING STORY

摘要

How can an in principal binary alloy of iron and carbon show so many fascinating phenomena and still today give surprises to users, foundrymen and researchers? This paper points out some critical steps in the understanding of the whole chain, from the melt to a cast iron product in service. The understanding of the material is gradually improved, assisted by the advances of other fields, e.g. analyzing methods and computational techniques. The heart in cast iron is the graphite, which is a highly difficult phase to understand but gives the material its unique properties. The linkage between understanding and modelling is necessary to calculate/simulate the processes occurring, where the precipitation, nucleation and growth of the different phases are the keys. Proper nucleation and growth models have been introduced to predict e.g. 1. primary precipitation of austenite and graphite; 2. eutectic growth of different morphologies of graphite or cementite and austenite; 3. solid state transformation of austenite into ferrite and pearlite in both grey and ductile irons. and now gives realistic microstructures and solidification curves for most practical cases. The microstructure formation models gives input to shrinkage and volume calculations to predict porosities, and to predictions of mechanical properties. By linking microstructure formation models, characterization models for mechanical properties and Finite Element Analysis (FEA) it is today possible to use local properties in simulations of the behavior of cast iron components. Many phenomena in cast iron, however, still remain unexplained. As one student labelled one of his experimental files on ductile iron, cast iron materials and simulations are indeed a never ending story, with a bright future in industrial applications.