Case-hardened steel part for use in aeronautics

A process for manufacturing a steel part for use in aeronautics

• comprising the consecutive steps of:
• a) providing a part comprising a substrate, the substrate comprising at least carbon, cobalt, aluminum and nickel, and having
• an average mass fraction of carbon comprised between 0.09% and 0.17%,
• an average mass fraction of cobalt comprised between 15.5% and 18.5%,
• an average mass fraction of aluminum of less than 0.1%, and
• an average mass fraction of nickel comprised between 7.2% and 9.8
• b) case-hardening the part in a controlled atmosphere at a temperature comprised between 900° C. and 1100° C.,
• 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.,
• wherein the case-hardening of step b) is carried out so that at least a portion of a surface of the part has an average mass fraction of carbon comprised between 0.4% and 0.6%, and wherein the aging comprises nitriding the part in an atmosphere comprising ammonia so that the part comprises a nitrided layer at least partially covering the substrate,
• nitriding being simultaneous with aging of the part,
• wherein the formation of the nitrided layer is made in a chamber and wherein the formation of the nitrided layer is controlled by imposing in the chamber a nitrogen potential Kn equal to 3 for one hour, followed by the imposition of Kn equal to 0.6 for 11 hours.