Aim of this paper is to analyze the effect of manganese percentages on steel compositions. Laboratory as cast materials, in particular designed for Quenching and Partitioning process (Q&P), are here considered. The considered steel chemical composition was that of a 0.15C with 1.5Si, two different Mn contents and with no significant Al content. Two-Step Q&P heat treatments were carried out in laboratory by means of dilatometric tests. X-ray diffraction measurements have been carried out aimed to assess the retained austenite volume fraction. The tensile properties of the quenched and partitioned materials were analyzed. Results showed a marked dependence of strength, ductility and strain capacity values on heat treatment conditions. In the case of higher austenite contents, higher uniform elongation values were found. Higher tensile properties were found in the case of higher Mn steel with respect to the lower Mn one. The main novelty of this paper consists in applying Q&P to low carbon (low hardenability steel) showing the effect of such a process on mechanical properties of steels usually adopted for automotive applications.