Creep strain growth behaviour of Hastelloy X above 800°C under thermal-stress cyclings

Abstract Actual structural components at high temperature are usually not only subjected to steady mechanical and cyclic loads but also accompanied by temperature variation. Creep ratcheting due to cyclic thermal stress is one of the typical examples. The creep strain growth behaviours of Hastelloy X above 800°C under thermal stress cyclings have been discussed. (1) Cycle dependent creep ratchet strain growth can be estimated to be α ΔT , where α is the thermal expansion coefficient and ΔT is temperature difference across a body. (2) Time dependent strain growth with temperature variation can be derived by time fraction, virtual activation energy and creep strain of the base temperature. (3) Decreasing creep rate will appear in the neighbourhood of 15–20% of rupture time and increasing creep rate will occur after this, which is almost linear on a logarithmic time scale and Hastelloy X shows softening behaviour on creep after exposure at the higher temperature.