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 degrees C and 316NG austenitic steel at both 500 degrees C and 600 degrees 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 degrees 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.