Evaluation of the Microstructure and Corrosion Resistance of the 800HT Alloy After Long-Term Operation

The development of renewable fuel-based energy, as well as waste disposal and advanced chemical processes, makes it necessary to use materials with favorable corrosion resistance, especially in high temperature conditions. In such conditions, alloys are subject to degradation, and the rate of the processes depends directly on the state of the material at the beginning of operation and the operating environment conditions. Hence, the 800HT material was selected for the tests, which was subjected to long-term operation in variable ambient conditions. This work aims to reveal the possibility of microstructure recovery in the alloy after long-term operation and subjected to detailed LM and SEM microscopic analysis and corrosion tests in simulated environments. The tests revealed that in long-term operation conditions, periods of temperature exceedance may occur and, as a consequence, unfavorable phases affecting the plasticity of the material, such as σ-phase or M23C6, may be released. In turn, the presence of these phases, mainly at grain boundaries, does not significantly reduce corrosion resistance in nitrogen-rich environments, but causes intensive processes induced by chlorides and sulfates at high temperatures.