Supplementary Performance Assessment of Additively Manufactured Alloy 718 After Heat Treatment Optimized for Oil and Gas Applications (C2026-00112)

Mark Yunovich

Alloy 718 is attractive for a wide range of applications within the petroleum and natural gas( PNG) industries. However, when produced via additive manufacturing (AM), components typically exhibit considerable residual stresses and compositional and microstructural heterogeneities that can adversely affect the performance. The current practice uses a solution annealing protocol prescribed in the API-6ACRA standard, which was designed for wrought material. Consequently, it cannot completely eliminate the AM solidification microstructure, which is essential to reliably achieve the required properties. An integrated computational materials engineering (ICME) framework, based on modeling tools and experimental validation, was used to design a more effective heat treatment for AM718. This optimized heat treatment produced microstructures and mechanical properties that were virtually identical to those of wrought material in the 825 MPa strength condition. The question is whether the AM processing affected the susceptibility to environmentally assisted cracking. AM and wrought specimens were given similar heat treatments and subjected to slow strain rate tensile tests at a nominal strain rate of 1x10-6/s in an inert environment, and after 100 h and 300 h pre-exposures in an acidified environment at controlled hydrogen fugacity. The results and details regarding the heat treatment and test methods will be presented.