This paper contains the results of a design optimization study performed on the steady-casting operation of the Columbus Stainless single-strand stainless steel caster tundish. Residence Time Distribution (RTD) data such as minimum residence time (or plug flow volume fraction) and dead volume are used as objective functions in the mathematical optimization process. Water is used in the first two case studies as modeling fluid to allow for comparison with water model results. Liquid steel is used in the last case study to investigate the effect of temperature and buoyancy on the resulting flow patterns and the optimum design. Two separate tundish configurations are considered. The first has one dam and one weir, while the second comprises a baffle with angled holes and an impact pad. Significant improvements of up to 34 % in minimum residence time are obtained for the second configuration.