US A-USC ComTest Demonstration of Large Superalloy Forging

The recently completed A-USC ComTest program, funded by the US Department of Energy, Office of Fossil Energy, demonstrated the domestic capability to make nominal 30,000 pound forgings for wye fittings and shaft rotors. Two relatively new age-hardened nickel-base superalloys, INCONEL alloy 740H1 and HAYNES 2822 alloy that were extensively charcterized in a previous A-USC program, were downselected for the applications respectively. Special Metals, Scot Forge and EPRI collaborated on this work. The potential challenges to making such large forgings include solidification segregation, thermal stress cracking, high forging loads and degredation of microstructure and properties during forging and heat-treatment.This paper reviews the manufacturing steps and proposed solutions to some of the quality issues that were encountered in these first article demonstrations. Microstructure and mechanical properties in 30-inch cross-section are summarized and compared to prior published data collected on relatively thin material. In general, the yield and tensile strength and hardness were reduced due to coarser grain and gamma prime size although they exceeded ASME code minima. Tensile ductility and impact toughness were acceptable. Limited creep-rupture testing indicated that long time creep strength may be independent of heat-treated cross section. A concluding discussion identifies additional testing that is needed for the design and qualification of large components for A-USC and sCO2 power systems. The remaining material from these forgings has been retained by DOE for future testing and evaluation. This project was funded by DOE OFE award DE-FE0025064 and was administered by NETL.

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