Compare white and nodular cast irons with respect to (a) composition and heat treatment, (b) microstructure, and (c) mechanical characteristics.

Question: Compare white and nodular cast irons in terms of (a) composition and heat treatment, (b) microstructure, and (c) mechanical characteristics. Answer: (a) White cast iron contains carbon in the form of cementite, while nodular cast iron contains carbon as graphite nodules. Heat treatment is more common in nodular cast iron, often subjected to annealing or normalizing to refine the microstructure and improve mechanical properties. (b) The microstructure of white cast iron consists of a matrix of pearlite and cementite, resulting in a hard, brittle material with little ductility. Nodular cast iron has graphite nodules dispersed throughout the ferritic or pearlitic matrix, which improves mechanical properties and reduces stress concentration points. (c) White cast iron is characterized by high hardness and wear resistance but low ductility and poor impact resistance. Nodular cast iron exhibits greater ductility and strength due to the presence of graphite nodules, making it more suitable for a wider range of applications such as automotive components, pipes, and machinery parts.