ANS:A - softens it to facilitate machining.

Annealing of cast iron softens it to facilitate machining. Annealing is a heat treatment process that involves heating the material to a specific temperature and then cooling it slowly to alter its microstructure and mechanical properties. In the case of cast iron, annealing is commonly performed to soften the material, making it easier to machine. Cast iron typically contains hard and brittle phases such as cementite (iron carbide) and pearlite. Annealing cast iron involves heating it to a temperature below its melting point (typically between 600°C to 900°C) and holding it at that temperature for a period of time, followed by slow cooling. This process causes the formation of softer phases such as ferrite and graphite, which improve machinability by reducing the hardness and brittleness of the material. Therefore, annealing of cast iron softens it to facilitate machining, making it easier to cut, drill, or grind to the desired shape or dimension.