Comparison of microstructures developed during solidification of undercooled tool steel in levitation and on a substrate

In this paper, the microstructures developed in highly undercooled samples from Cr-Mo-V tool steel of ledeburite type during non-equilibrium solidification in levitation and on a copper substrate are compared. The microstructures in spherical samples solidified during levitation are dependent on the level of undercooling reached prior to spontaneous nucleation. In the whole volume of a single rapidly solidified sample, microstructures are quasi-homogeneous. Rapidly solidified splat samples were prepared using copper substrate solidification from the melt with various initial undercooling. As an example, the microstructure in the sample solidified from the initial undercooling of 100 K with morphologically different microstructural regions is presented. Carbides of solidification origin with different size, morphology and location were found in samples solidified in levitation and on a substrate as well.