Strain controlled LCF behaviour of SA-333 Gr 6 piping material in the range 298-673 K

Abstract

The low cycle fatigue (LCF) behaviour of carbon steel SA-333 Gr 6 alloy has been investigated between 300 and 673 K employing a triangular waveform at a strain rate of 5 × 10^-3 s^-1. The cyclic stress response varied as a complex function of temperature. Dynamic strain ageing (DSA) was found to occur over a temperature range between 473 and 623 K. In this DSA domain, the alloy exhibited marked cyclic hardening with a pronounced maximum at 623 K. Additionally the alloy displayed negative strain rate sensitivity of cyclic stress in the DSA regime. The temperature dependence of LCF life showed a maximum at ~523 K. The drastic reduction in life between 523 and 673 K has been ascribed primarily to the deleterious effects of DSA on crack initiation and propagation, while the lower life at temperatures less than 523 K has been attributed to the larger cyclic response stress. The influences of DSA on strain-life relationships, cyclic stress-strain curves and fracture behaviour are discussed.