Since the cooling rate in normalizing heat treatment is not controlled, the resulting organization depends on the thickness of the steel workpiece. Therefore, the effect of improving mechanical properties is greater in thin workpieces.
Normalized steels have higher hardness and strength than annealed steels due to the following reasons.
The pearlite content in normalized steels is higher than in annealed steels with the same carbon content due to the shift of the eutectic constituents to lower values.
The dispersion of the pearlite and ferrite phases is finer.
The pearlite in normalized steel is finer and the layer spacing is smaller than in annealed steel.
