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 ∼50b3 while PM2000 has ∼100b3. 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.