This annealing process is applied to improve irregular, inhomogeneous and coarse grained structures in for example, castings, forgings or rolled sheet. This improves the mechanical properties of the material by obtaining a fine-grained structure with grains of roughly equal size and a round shape.
To achieve those results, the workpieces are usually brought up to temperature quickly and held at the target temperature for a certain amount of time. This time at temperature and the temperature itself will vary and is dependent on the base material. Once the material is fully austenitized, the cooling needs to take place. It is of great importance – and in contrast to the hardening in which a rapid cooling (/quenching) is required to force steel to transform into a martensite structure – that in normalizing the cooling occurs in a slow and controlled manner. This will result in a ferrite and pearlite structure for hypoeutectoid steels and a structure of pearlite and cementite at the grain boundaries for hypereutectoid steels.
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