Remelting experiments on the laboratory scale with special reference to grain refinement of the high alloyed steel grades X1CrNiMoCuN20-18-7, X5CrNiNb18-10 and X40CrMoV5-1 have been conducted in partnership between the Böhler Edelstahl GmbH & Co KG and the Chair of Ferrous Metallurgy in Leoben/Austria. The aim of the experiments was to achieve a fully equiaxed, refined as-cast structure by heterogenous nucleation. A literature study was carried out in order to find favourable nucleation sites for the investigated steel grades. The results showed that nonmetallic inclusions containing rare earths seem to be the most favourable nucleation sites for the investigated steel grades. A commercial available Fe-Si-Cr-Ce-prealloy containing 13% cerium was therefore used as grain refiner. Several remelting experiments were processed to investigate the effect of cerium containing inclusions on the as-cast structure. The weight of the laboratory-ingots varies between 200 g and 12 kg. The microstructure of the samples was visually investigated after cutting and etching. Ingots with clearly visible grain refined zones were further investigated by SEM-microscopy. Nonmetallic inclusions were analysed and particle densities were measured. The as-cast structure of the steel grade X1CrNiMoCuN20-18-7 could be refined by Cerium addition at higher Al contents. Ingots without cerium addition show large columnar primary grains, whereas the grain refined ingots have small equiaxed grains. AlCeO3-inclusions were identified as effective nucleation sites in the austenitic steel. Die other steel grades X5CrNiNb18-10 and X40CrMoV5-1 could not be grain refined by cerium additions. The reason for the ineffectiveness of the cerium containing inclusions in these steel grades is their deltaferritic solidification. The misfit between the deltaferritic primary grains and the cerium containing inclusions is larger than the misfit between austenite and AlCeO3.