Influences of Nano-structured Thermal Stability on the Intergranular Corrosion of High-Carbon Austenitic Heat-Resistant Steel

摘要

The influences of nano-structured thermal stability on the intergranular corrosion (IGC) of Super304H steel were investigated by electrochemical tests and surface analysis in this study. It was found that IGC in nano-twinned (NT) Super304H SS during the aging process was governed by the formation of nano-scale M23C6 precipitates, which generated Cr-depletion zones, and fast healing of the Cr-depletion zones due to the rapid infusion of Cr atoms from the matrix. Conversely, the nano-grains (NG) with poor thermal stability could accelerate the nucleation of sigma phase at recrystallizing interfaces after short-time aging at 650 degrees C, thereby deteriorating the IGC resistance. The thermal stability of the NT structure was superior to that of the NG structure, which preserved the IGC resistance of Super304H SS during the aging process. Therefore, it was critical to keep the SP strain below the saturation value to achieve high thermal stability, good IGC resistance, and suppression of recrystallisation-induced precipitation.