Thick gauge strip production using thin slab casting and direct rolling(TSDR)technologies show important challenges due to the lack of high total reduction from slab to final strip.In these cases,a correct design of the reductions in the first rolling passes is an important tool to achieve an optimized through-thickness homogenization in the final product.There are metallurgically key thicknesses where an optimized per pass reduction should be taken to result in an optimized homogenization of the through-thickness austenite grain(austenite conditioning)setting up the stage for the final metallurgy and ferrite grain transformation.This proper per pass reduction design can be called taking a “critical reduction at a critical thickness”.This paper shows how the combination of finite element analysis and microstructural evolution models help understand the strain distribution after each rolling pass and the improvement in strain penetration to the centerline area when an optimum reduction schedule is selected.The analysis,applied to a niobium microalloyed grade,provides useful information for,not only mean grain size refinement in the centerline area,but also an improvement in the homogenization of the grain size distribution.Following these concepts of taking a “critical reduction at a critical thickness”,an improvement in both strength and toughness properties could be achieved in the final TSDR rolled product.In fact this very basic metallurgical principle can and has been applied to the metallurgy of producing plate,traditional hot strip coil and long product section sizes.