Impacts of Applied Stresses on High Temperature Corrosion Behavior of HR3C in Molten Salt

The corrosion behavior of austenitic steel HR3C in Na2SO4-K2SO4 molten salt and the impacts of applied stresses were studied at 700 and 750 A degrees C. The corrosion behavior was investigated through measurements of oxide morphology, depth of the oxidation layer, and the compositional changes. It was determined that the corrosion resistance of HR3C to the molten salts was strongly related to the formation of the outer oxide layer. When there was no stress, a stable and dense Cr2O3 layer was formed at 700 A degrees C, which implied superior corrosion resistance, while at 750 A degrees C, the external oxide layer was dissolved with the molten salt and internal sulfidation reactions happened. An imposed applied stress generally led to a larger chromium ratio in a denser outer oxide layer, and an overall thinner corrosion layer. With the value of the stress increased from 20 to 40, and to 60 MPa, the influence became stronger. These consequences are mostly attributed to a greater concentration of dislocations and defects in the specimens under applied stresses. These defects act as fast diffusion paths for the Cr atoms to diffuse to the surface, and thus, promote a faster formation of the protective Cr2O3 oxide layer.