Steel castings should be used after heat treatment. Because there are casting defects such as porosity, cracks, shrinkage cavity and shrinkage porosity, coarse grains, uneven structure, and residual internal stress in the steel castings in the as-cast state, the strength, especially the plasticity and toughness of the steel castings are greatly reduced.

In order to refine the crystal grains, uniform structure, and eliminate internal stress, steel castings must be normalized or annealed. Normalized steel has higher mechanical properties and lower costs than annealed steel, so it has more applications. However, because normalizing treatment will cause larger internal stress than annealing, it is only suitable for steel castings with a carbon content of less than 0.35%.

Because low-carbon steel castings have good plasticity, they are not easy to crack during cooling. In order to reduce internal stress, steel castings should be tempered at a high temperature after normalizing. For steel castings with carbon content ≥0.35%, complex structure and easy to crack, only annealing treatment can be carried out. Steel castings should not be quenched, otherwise, they will easily crack.