Internal oxidation and crack susceptibility of alloy 310S stainless steel after long term exposure to supercritical water at 500 °C

•High temperature oxidation of alloy 310S stainless steel in supercritical water (SCW).•Micro-crack initiation in alloy 310S stainless steel exposed to SCW (500°C/25MPa).•Oxide layers including Fe3O4 (outer), Fe-Cr spinel (inner), [Mn,Cr]2O3 (transition).•Carbide formation and Cr depletion resulted in grain boundary embrittlement.•Crack tip was filled with Cr, O, C and Si elements while depleted from Cr and Fe.