Stress relaxation behavior of nanocluster-strengthened ferritic alloy at high temperatures

Stress relaxation behavior was investigated for the nanoclusters/ dispersoids-strengthened steels including the nanostructured ferritic alloy 14YWT (SM10), oxide-dispersion strengthened (ODS) Eurofer97, and commercial ODS steel PM2000. The stress relaxation tests were carried out at high temperatures ranging from 600 to 1000°C. Overall, the relaxation rates of 14YWT and ODS-Eurofer97 were lower than that of PM2000. To analyze the strain rate sensitivity of the alloys, the load drop-time curves were converted to the stress-strain rate curves. In the log-log plots of these curves, no significant change in slope was observed in the strain rate range of 2 × 10 ^-5-1 × 10 ^-3s ^-1. At 600°C, 14YWT and ODS-Eurofer97 have similar activation values of ∼50b ³ while PM2000 has ∼100b ³. Above 700°C, the differences of the activation energy among alloys become more noticeable with increasing temperature. The activation energies of the three alloys were derived and compared. The rate-controlling mechanisms in the stress relaxation of the three nanoclusters/dispersoids-hardened alloys include dislocation glide and climb, and further study is necessary to clarify detailed contributing mechanisms.