Creep properties and TEM characterization of 347H stainless steel

Creep properties of a recent 347H austenitic stainless steel plate at 1073 K (800°C) and 1123 K (850 °C) were examined, and microstructural evolution under temperature and creep was characterized using TEM. Creep minimum rate vs. stress plot at 1123 K (850 °C) showed two different slope regions, suggesting a change in the creep-rate controlling mechanism at lower stresses. Detailed TEM characterization showed that in high-stress (or short-term) creep tests, NbC precipitates interacted with dislocations and indicated to slow down the dislocation-controlled creep by orienting towards slip directions. In low-stress (long-term) creep tests, formation of ferrite on NbC was observed and no sigma phase was detected. In long-term low stress creep tests, NbC precipitates gave way to formation of Widmanstatten Cr₂N and Z-phase precipitates, and the rate-controlling mechanism may change to grain boundary sliding. (author)