Effect of preconditioning on the microstructure and mechanical properties of ductile cast iron

The effect of preconditioning and optimizing the quantity of ladle addition on improving the microstructure and mechanical properties of thin wall ductile cast iron (TWDCI), with particular attention on the chilling tendency of ductile cast iron (DCI), has been studied. Comparative studies were conducted on the basis of the best quantity of preconditioner to be added during the ladle treatment in order to improve the microstructure and mechanical properties of the resulting ductile cast iron. ASTM A834-95 (2001) standard on open ladle treatment was adopted where preconditioner (Al,Zr - FeSi) of 0.05, 0.10 and 0.15 wt% were added to the nodularizer (10 % Mg-FeSi) in the treatment ladles. Nodules and nodularity of the DCI were observed and the results obtained were measured and correlated with the results obtained from the hardness and tensile tests. The optimum effect of the preconditioner was observed at 0.1 wt% of ladle addition, where the tensile strength of the unpreconditioned melt was increased from 385 MPa to 420 MPa, yield strength from 250 MPa to 290 MPa and the percentage elongation from 16 to 20 %, which resulted in ductile cast iron with reduced carbide formation and improved nodule counts.