In the present work the relations between microstructure, cleanliness and solidification parameters of the low alloyed and high alloyed steels in the case of rapid solidification have been investigated. Rapid solidification was investigated experimentally under laboratory conditions by immersion of a cold copper rod into a steel bath. Samples from the frozen steel shell were investigated under an optical microscope. As a structure-relevant characteristic, the secondary dendrite arm spacing (SDAS) and the nonmetallic inclusion diameter have been obtained as a function of the distance from the contact area and the solidification conditions.