Tensile Properties of Ferritic and Austenitic Alloys after Elevated Temperature Stressed-Exposure in Simulated HTR-Helium Coolant: A Cooperative International Study

More than 20 different ferritic and austenitic commercial alloys of potential application in Gas-Cooled Reactors were tensile tested at room and elevated temperatures after stressed-exposures of up to almost 20000 hours under appropriate conditions in simulated reactor coolant. These exposures were initiated at CIIR/Oslo by the Dragon Reactor Project and the postexposure testing and evaluation were conducted by EIR, GAC, ORNL and HTMP. Most of the alloys experienced significant decreases in their levels of total elongation and reduction in area as a result of exposure but generally still retained ductilities in the range 20 to 25% (measured as reduction in area). Yield and ultimate tensile strength were affected considerably less than were ductilities. Changes in tensile properties were related to exposure temperature, time and environment as well as to creepstrain accumulated during the exposure. Results for two classes of austenitic stainless steels and for Alloy 800 were further examined to illustrate a type of acceptability criterion, based on mechanical work to fracture, which could be provided to the designer as a guide for selection of materials. Examples based on the data obtained in this study and assumptions of minimum required ductility are presented and discussed. (author)