The primary purpose of this research is to investigate the effects of chemical compositions and selected processing parameters, including nodularization treatment, post inoculation, pouring time and pouring temperature, on microstructures (nodularity, nodule count and pearlite percentage) and mechanical properties (tensile strength, yield strength, elongation and low temperature impact value) of key cast components used in large-scale windmills. This study has established the optimal alloy design and process conditions for different targeted castings. In addition, regression analysis had been performed to correlate the mechanical properties with chemical compositions and microstructures. The attained regression equations can be used to obtain the appropriate alloy design for castings with specified specification. Furthermore, by employing these regression equations, the mechanical properties can be predicted based upon the chemical composition and microstructure.