Effects of Si, Mn on the corrosion behavior of ferritic–martensitic steels in supercritical water (SCW) environments

Ferritic–martensitic (F/M) steels with various amounts of alloying elements (Cr: 12 wt. %, Si: 0.6–2.2 wt. %, Mn: 0.6–1.8 wt. %) were exposed to supercritical water (SCW) environments at 500 °C and 25 MPa for up to 1000 h. Gravimetric, Scanning Electron Microscope, Transmission Electron Microscopy (TEM), Energy-dispersive X-ray Spectroscopy (EDX) and X-ray Diffraction (XRD) analyses were conducted to characterize the corrosion behavior of F/M steels in supercritical water. The results showed that the contents of the alloying elements (Si, Mn) affected both the oxidation kinetics and the oxidation scales formed on F/M steels. The F/M steel (Si: 0.6 wt. %, Mn: 1.8 wt.%) showed the highest corrosion rate in SCW with an intermittent oxide scale formed on the surface. Increasing the Si content in F/M steel improved the oxidation resistance and promoted the formation of a uniform oxide scale. The mechanism associated with the corrosion of these F/M steels under SCW conditions is discussed.