The different solidification processes occuring in steels can be well studied by using the microstructure investigation. The microstructure can be observed after the sample preparation by using a special type of Oberhoffer etching. The changes in the cooling rate can be described by determining the secondary dendrite arm spacing. A relative cooling rate can be calculated by applying the relationship between the secondary dendrite arm spacing and the cooling rate which characterises the changes of cooling conditions in the ingot during the solidification.