Standard Specification for Vacuum-Treated Alloy Steel Forgings for Turbine Rotor Disks and Wheels

This specification covers vacuum-treated alloy steel forgings intended for use as turbine rotor disks and wheels. The steel shall be made by the basic electric-furnace process. The molten steel shall be vacuum treated using either the vacuum stream degassing process, vacuum-lift process or ladle degassing process prior to or during the pouring of the ingot in order to remove objectionable gases, particularly hydrogen. The forgings shall receive their hot mechanical work under a press, hammer, or mill of sufficient power to work the metal throughout its section. Before reheating for heat treatment, the forging shall be allowed to cool in a manner to prevent damage and to accomplish transformation. The forgings shall be heated to a suitable temperature for a sufficient length of time for complete austenitization and shall be tempered to develop the specified properties. The forgings shall be preliminarily machined on all surfaces prior to heat treatment and shall be stress relieved after machining. To measure some mechanical properties, the specimens shall be subjected to tension test, impact test, and hardness test. A non-destructive test like an ultrasonic inspection shall be made on all available surfaces to demonstrate freedom from detrimental internal indications.