Heat treatment is a process used to alter the physical and mechanical properties of materials such as metals and alloys. In the context of casting, heat treatment is often performed to improve the strength, hardness, and durability of the casted part. There are several heat treatment processes that can be used for casting, including carburising, normalising, annealing, and tempering. Among these options, the correct answer for the heat treatment process used for casting is normalising.

Normalising:
Normalising is a heat treatment process that involves heating the casting material to a temperature above its critical point, holding it at that temperature for a specific period of time, and then allowing it to cool in still air. The purpose of normalising is to refine the grain structure of the material, improve its mechanical properties, and relieve internal stresses. This process is typically performed after casting to eliminate any defects or irregularities in the microstructure of the material.

Carburising:
Carburising is a heat treatment process used to increase the carbon content at the surface of a material. It involves heating the casting in a carbon-rich environment, such as a carbonaceous gas or a solid carbon medium, to allow carbon atoms to diffuse into the surface of the material. Carburising is commonly used to improve the hardness and wear resistance of castings, particularly in applications where high surface hardness is desired.

Annealing:
Annealing is a heat treatment process that involves heating the casting material to a specific temperature and then cooling it slowly to room temperature. The purpose of annealing is to reduce the hardness and brittleness of the material, improve its machinability, and relieve internal stresses. This process is often used to restore the ductility and toughness of castings that have undergone previous heat treatment processes.

Tempering:
Tempering is a heat treatment process used to relieve the internal stresses in a material that has been hardened by quenching. It involves heating the casting to a specific temperature below its critical point and then cooling it slowly. Tempering is typically performed after carburising or quenching to improve the toughness and reduce the brittleness of the material.

In conclusion, the correct heat treatment process used for casting is normalising. This process helps refine the grain structure, improve the mechanical properties, and relieve internal stresses in the casted material.