A process for manufacturing a steel part for use in aeronautics comprising the consecutive steps of: a) providing a part comprising a steel substrate, the substrate being made either in ferrium C61 or in ferrium C64, and comprising for the ferrium C61: - an average mass fraction of carbon comprised between 0.13% and 0.17%, - an average mass fraction of cobalt comprised between 17.5% and 18.5%, - a sum of the average mass fraction of molybdenum and the average mass fraction of tungsten comprised between 0.9% and 1.3% and - an average mass fraction of nickel comprised between 9.2% and 9.8, or comprising for the ferrium C64: - an average mass fraction of carbon comprised between 0.09% and 0.13%, - an average mass fraction of cobalt comprised between 15.5% and 17%, - an average mass fraction of aluminum less than 0.1%, and - an average mass fraction of nickel comprised between 7.2% and 7.8, b) case-hardening the part in a controlled atmosphere at a temperature comprised between 900°C and 1100°C, so that at least a portion of the part has an average mass fraction of carbon comprised between 0.4% and 0.6%, c) quenching the part and cryogenically treating the part in a controlled atmosphere at a temperature comprised between -50°C and -100°C, and d) aging the part in a controlled atmosphere at a temperature comprised between 450°C and 550°C, characterized in that the aging comprises nitriding the part in an atmosphere comprising ammonia so that the part comprises a nitrided surface, nitriding being simultaneous with aging of the part and the nitrided layer thus obtained having a thickness comprised between 5 μm and 180 μm, preferably comprised between 50 μm and 150 μm, an average mass fraction of carbon comprised between 0.4% and 0.6% and an average mass fraction of nitrogen comprised between 0.6% and 3%. a) providing a part comprising a steel substrate, the substrate being made either in ferrium C61 or in ferrium C64, and comprising for the ferrium C61: - an average mass fraction of carbon comprised between 0.13% and 0.17%, - an average mass fraction of cobalt comprised between 17.5% and 18.5%, - a sum of the average mass fraction of molybdenum and the average mass fraction of tungsten comprised between 0.9% and 1.3% and - an average mass fraction of nickel comprised between 9.2% and 9.8, or comprising for the ferrium C64: - an average mass fraction of carbon comprised between 0.09% and 0.13%, - an average mass fraction of cobalt comprised between 15.5% and 17%, - an average mass fraction of aluminum less than 0.1%, and - an average mass fraction of nickel comprised between 7.2% and 7.8, - an average mass fraction of carbon comprised between 0.13% and 0.17%, - an average mass fraction of cobalt comprised between 17.5% and 18.5%, - a sum of the average mass fraction of molybdenum and the average mass fraction of tungsten comprised between 0.9% and 1.3% and - an average mass fraction of nickel comprised between 9.2% and 9.8, - an average mass fraction of carbon comprised between 0.09% and 0.13%, - an average mass fraction of cobalt comprised between 15.5% and 17%, - an average mass fraction of aluminum less than 0.1%, and - an average mass fraction of nickel comprised between 7.2% and 7.8, b) case-hardening the part in a controlled atmosphere at a temperature comprised between 900°C and 1100°C, so that at least a portion of the part has an average mass fraction of carbon comprised between 0.4% and 0.6%, c) quenching the part and cryogenically treating the part in a controlled atmosphere at a temperature comprised between -50°C and -100°C, and d) aging the part in a controlled atmosphere at a temperature comprised between 450°C and 550°C, characterized in that the aging comprises nitriding the part in an atmosphere comprising ammonia so that the part comprises a nitrided surface, nitriding being simultaneous with aging of the part and the nitrided layer thus obtained having a thickness comprised between 5 μm and 180 μm, preferably comprised between 50 μm and 150 μm, an average mass fraction of carbon comprised between 0.4% and 0.6% and an average mass fraction of nitrogen comprised between 0.6% and 3%. characterized in that the aging comprises nitriding the part in an atmosphere comprising ammonia so that the part comprises a nitrided surface, nitriding being simultaneous with aging of the part and the nitrided layer thus obtained having a thickness comprised between 5 μm and 180 μm, preferably comprised between 50 μm and 150 μm, an average mass fraction of carbon comprised between 0.4% and 0.6% and an average mass fraction of nitrogen comprised between 0.6% and 3%.