Corrosion Behavior of Steel T91 and HR3C in 600 ℃/25 MPa Supercritical CO₂ Environment

In order to study the applicability of heat-resistant steel in supercritical carbon dioxide Brayton cycle system, two metal materials commonly used in power plants (martensitic steel T91 and austenitic stainless steel HR3C) were selected and used in corrosion tests in supercritical carbon dioxide environment of 600 ℃/25 MPa. The corrosion kinetics of the two materials was studied by corrosion mass grain. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used to measure the thickness of the corrosion product layer, and analyze the morphology and element distribution of the corrosion product. The phase of corrosion product on the surface of samples was analyzed by X-ray diffraction (XRD). The results show that in supercritical carbon dioxide, the corrosion mass grain of martensitic steel T91 and austenitic stainless steel HR3C displayed an approximate parabolic change with time. And the steel HR3C had better corrosion resistance than steel T91 obviously. The corrosion product of T91 consisted of inner layer (FeCr₂O₄), outer layer (Fe₃O₄), and a transition area between corrosion product and metal substrate (mixture of FeCr₂O₄ and substrate). The corrosion product on the surface of steel HR3C was a protective Cr₂O₃ oxide layer.