Tensile and Impact Properties of Candidate Alloys for High-Temperature Gas-Cooled Reactor Applications

The tensile properties of solution-treated Incoloy alloy 800H, Hastelloy-X, Nimonic-86, and Inconel-617 have been determined in the temperature range 20 to I000°C. The strength parameters at temperatures above 700°C showed a strong dependence on the strain rate; at low strain rates the deformation was dominated by creep effects, the strain rate and maximum stress being related by the Norton creep equation. The tensile and impact properties of the alloys were also determined after exposure at 700 to 1000°C for up to 30 000 h. For Incoloy-800H, the results showed good retention of ductility and impact strength. The nickel-base alloys, in contrast, were found to have low room-temperature impact resistance after long time exposure at 700 to 900 °C, typical values being 10 to 20 J. cm⁻². In impact tests at the exposure temperature, impact strengths were generally above 50 J.cm⁻². At room temperature, allowances in design must be made for the low impact strength of the nickel-base alloys to ensure against brittle fracture. For example, excessive stresses during cooling of components following shutdown should be avoided.