The filling sequence, solidification and solid state transformation in this casting have been simulated using a FDM-program with models for nucleation and growth of all relevant phases. To verify the models, a redesigned plate casting was cast with a nodular iron containing 4.00 % silicon. It is shown that the action of silicon on the ferrite growth only is related to the transformation temperature, which drastically increases when the silicon content more » is raised. The results have been the basis for the derivation of a new growth model for the ferrite during an interface controlled stage.
The cooling curves were analyzed by thermal analysis in order to derive the transformation kinetics for the ferrite growth. Plate castings (3 to 50 mm) have been cast with five different silicon contents (1.7 to 4.9%). This is a promising way to obtain nodular iron castings with desirable and predictable properties. However, due to the solution hardening of ferrite by silicon, a good strength is obtained. When increasing the silicon content up to a level of about 3.5 to 4%, the structure will usually be predominantly ferritic. The result is usually a casting with a considerable variation in ferrite/pearlite ratio in different parts due to the variation in thermal history. Nodular cast iron is often alloyed with pearlite-promoting elements, such as Mn, Cu or Sn, to increase the strength. Silicon is commonly used in nodular cast iron due to its graphitizing and ferritizing effect.
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