Abstract: Planar disregistries between various substrates and nucleated phases during liquid steel solidification were calculated. The relation between lattice disregistry and heterogeneous nucleation catalysis of liquid steel was analyzed. The results show that the smaller the disregistry is, the more effective the substrate is for promoting nucleation. The logarithm of undercooling is approximately linear with the disregistry between the substrate and the nucleated phase. A substrate is presumed as the highly effective nucleus for promoting nucleation if the disregistry between the substrate and the nucleated phase is lower than 8%.