| Inconel 718 is a Ni-Fe-based superalloy that has been central to the gas turbine industry since its discovery in 1963. While much more difficult to process than carbon or stainless steels, among its superalloy peers Inconel 718 has relatively high forgeability and has been used to make discs, rings, shells, and structural components. A metal forming process design algorithm is presented to incorporate key criteria relevant to superalloy processing.;This algorithm was applied to conceptual forging and heat treating extremely large rings of Inconel 718 of diameter 1956 mm (77in) and weight 3252 kg (7155 lb). A 3-stage standard thermomechanical (TMP) processing was used, where Stage 1 strain varied from 0.1190 to 0.2941, Stage 2 from 0.0208 to 0.0357 and Stage 3 from 0.0440 to 0.0940. This was followed by heat treatment of a solution anneal (954°C/1750°F for 4 hour hold), air cool, then a double aging (718°C/1325°F for 8 hour hold; furnace cool to 621°C/1150°F @ 56°C/100°F per hr; 18 hour total time for both steps). Preliminary mechanical testing was performed. Average yield strength of 951 MPa/138 ksi (longitudinal) and 979 MPa/142 ksi (axial) was achieved. Tensile strengths were 1276 MPa/185 ksi (longitudinal) and 1255 MPa/182 ksi (axial). Elongations and reduction of areas attained were, respectively, 18 (long) and 25 (axial) and 28 (long) and 27 (axial). |
