Tension–torsion ratcheting tests on 9Cr steel at high temperature

• Ratcheting tension–torsion tests were made on 9Cr specimens at 450 °C and 550 °C.
• RCC-MRx efficiency diagram gives cumulative strains lower than experimental ones.
• Limitation of ratcheting must be related to the allowable strain limits for this material.

Because of their good thermo-physical properties, 9Cr steels are being considered as structural materials for fusion and fourth generation nuclear reactor components.However, these materials feature a particular behaviour in strain hardening, they present a very limited ductility and soften under cyclic load. This study contributes to an evaluation of the extent to which component design rules written for materials with a greater ductility and which have a better behaviour under cyclic load, are applicable to this material.This article investigates ratcheting in cyclic torsion–tension tests made on 9Cr steel specimens at 450 °C and 550 °C. The results shows that the RCC-MRx efficiency diagram does not form a lower envelope representative of the worst results for tests made using 9Cr steel. Use of this diagram in its present form would lead to estimated cumulative strains lower than experimentally observed strains. This work is a first step towards the definition of a modified efficiency diagram suited for 9Cr steel.