In the present investigation, the effect of both: rolling parameters (2 reduction rates and 3 cooling rates) and chemical elements such as: C, Mn, Nb, Ti, Mo, Ni, Cr, Cu and B, has been studied in relation to strength properties in low-carbon microalloyed steels with high niobium contents (up to 0,12 wt.% Nb). For this purpose, an experimental set-up was designed based on an intelligent design of experiments (DoE), resulting in 26 casts (laboratory casts). A combination of metallography, Electron Back-Scattered Diffraction (EBSD) and tensile tests have been performed to study how processing parameters and chemical composition affect the strength. The results, where the proof stress, tensile strength, uniform and fracture elongations are the response variables, have been analysed statistically by means of multiple linear regression technique, leading to response equations. From the results, it was found that the effectiveness of niobium increasing the strength is reduced as carbon content increases.