Heat treatment of steel is done to mainly change its __________ properties.

ANS:C - mechanical

Heat treatment of steel is primarily done to change its mechanical properties. During heat treatment, steel is subjected to controlled heating and cooling processes to alter its microstructure, which in turn affects its mechanical properties such as hardness, strength, toughness, and ductility. Different heat treatment techniques, such as annealing, quenching, tempering, and normalizing, are used to achieve specific combinations of these properties to suit the desired application requirements. While heat treatment may indirectly affect other properties such as physical and surface characteristics, its primary objective is to modify the mechanical properties of the steel to enhance its performance in various applications.