Effects of dwell location on the creep-fatigue endurance of cast Type 304L

Abstract

Thermo-mechanical cycling leads to creep-fatigue cycles in which the dwells can be in a variety of positions. In-phase cycling gives dwells at the peak. Out of phase cycling (by 180°) gives compressive dwells and 90° phase cycling gives a cycle in which the dwell is at an intermediate position within the cycle. Furthermore, components often experience cycles with a variety of different strain amplitudes and the creep dwells do not experience pure strain control but may contain elastic follow-up. To investigate the effects of these different factors on creep-fatigue endurance a series of isothermal tests have been conducted on Cast 304L steel at 650°C. These tests were then analysed using the British Energy R5 procedure, which was found to be overly conservative for tests with compressive dwells and for tests with dwells at an intermediate position within the cycle. This paper describes alternative approaches, for these types of cycles that give improved predictions of failure.

Keywords:

• creep
• ductility
• creep-fatigue
• ductility exhaustion
• creep damage
• Cast 304L