Short-range ordering kinetics in 316 austenitic stainless steel

In situ measurements are reported of electrical resistance changes in 316 austenitic stainless steel after abruptly raising or lowering temperature in the range from 440 °C to 550 °C subsequent to equilibration. These changes are found to be reproducible and have a magnitude roughly proportional to the temperature change. They are believed to be manifestations of approach toward a new state of shortrange order at the new temperature. Analysis of the kinetics indicates that very nearly a simple first-order reaction is involved. The rate constants were found to have an activation energy of 3.18 ± 0.40 eV. By analogy with the Zener relaxation, the temperature-change-induced short-range order which we observe is also believed to result from local atomic rearrangements in which an average atom makes a relatively small (<10) number of jumps. Good agreement between our measured relaxation rates and those calculated from extrapolated diffusion studies for iron, chromium, and nickel in comparable alloys tends to substantiate the hypothesis that average atomic jump rates are being measured.