A thermal analysis of thin strip steel casting has been conducted for planar flow casting. For a given strip thickness, the interface heat transfer coefficient, hi, has the most significant influence on average cooling rate ξavg (C/sec) and local solidification time tf. As a result, hi affects the as-cast structure and its properties. However, other factors such as melt superheat and initial substrate temperature have distinct but smaller effects on ξavg and tf. In addition, a decreasing hi makes initial isotherm movement slower and increases the delay time needed for the formation of certain types of segregation. Owing to a variation of local solidification time tf (because of cooling from one side only) there is a likely gradient of micro-structure across the thickness resulting in property variation through the steel strip thickness.