en Research Paper Research Paper Four compositions of austenitic Mn-Cr steels have been developed successfully for in-vessel component materials in power plant industry. The phase stability of these Mn-Cr steels was studied by and X-ray diffraction (XRD) patterns. XRD patterns have shown that the matrix of these Mn-Cr steels is a single γ-phase structure. The potentiodynamic polarisation curves suggested that these fabricated Mn-Cr steels showed passive behaviour in 0.1M H2SO 4solution. Therefore, semiconducting behaviour of passive film formed on these fabricated Mn-Cr steels in 0.1M H2SO 4 solution was evaluated by Mott–Schottky analysis. This analysis revealed that passive films behave as n-type and p-type semiconductors. Based on the Mott–Schottky analysis, it was also shown that donor and acceptor densities are in the order of 1021 cm -3 and are comparable for other austenitic stainless steels in acidic environments Low activation, Mn-Cr steel, XRD, Mott–Schottky 20 27 http://ijmse.iust.ac.ir/browse.php?a_code=A-10-127-59&slc_lang=en&sid=1 A Fattah-alhosseini a.fattah@basu.ac.ir 180031947532846002827 180031947532846002827 Yes Faculty of Engineering, Bu-Ali Sina University, Hamedan, Iran. M Asadi Asadabad 180031947532846002828 180031947532846002828 No Materials Research School, Nuclear Science and Technology Research Institute, Isfahan, Iran.