High solidification velocities, high temperature gradients and strong melt flow characterize the first moments of solidification in a continuous caster. The beginning of shell growth in the meniscus area is determined by the local heat flow, the strength of the shell and the fluid dynamics. In this region of the process, surface defects such as oscillation marks form, which influence the shell growth processes in the mould. Phase (ferrite/austenite) and microstructure selections (cells/dendrites) operate in this part of the process and control microsegregation, mechanics and defects of the surface region of the product. One of the most serious problems is hot cracking and a proper control of the casting parameters and of the steel composition is essential for obtaining high quality products. Stainless steels are highly sensitive to these phenomena. Control of deformation of the solid with a mushy zone is also of great importance as it is an input for machine design.