Study on mechanical degradation of Ferrite/ martensite and austenitic steels in high-temperature supercritical carbon dioxide environment

The mechanical degradation mechanism of T91 ferrite/martensite steel at 500 °C and 316NG austenitic steel at both 500 °C and 600 °C in supercritical carbon dioxide were investigated in detail by slow strain rate tensile tests and first-principles calculations of the adsorption and dissociation of CO2. In high-temperature CO2 atmosphere, CO2 could spontaneously dissociate into CO and O, and the spontaneously and partially dissociated O atoms exhibited a strong interaction with Cr. As the temperature was increased to 600 °C, the partial dissociation of CO2 occurred more rapidly and the ultimate tensile strength and total elongation of 316NG steel decreased significantly as well. Furthermore, a composite failure mode with intergranular brittle fracture and ductile fracture was investigated.