Investigation of anisotropic hardening response in a 12Cr-ODS ferritic steel subjected to 2.8 MeV Fe2+ irradiation

Abstract The anisotropic hardening response in a 12Cr-ODS ferritic steel was investigated before and after irradiation with 2.8 MeV Fe2+ at room temperature up to displacement damages of 0.5 and 15 dpa. For post irradiation examination, techniques of nano-indentation and orientation imaging microscopy were jointly applied to link crystal orientation with nano-hardness. Results showed that the averaged hardness of normal direction-transverse direction (TD-ND) specimen is less than that of rolling direction-transverse direction (RD-TD) specimen irrespective of the dose of irradiation damage. However, the amount of irradiation-induced hardening is observed to be weaker in TD-ND specimen relative to RD-TD specimen. These anisotropic phenomena are considered to be mainly attributed to the elongated grain structure with a very high grain aspect ratio of the present steel, in which smaller-sized grains are exhibited in TD-ND plane nevertheless fairly coarse grains are in RD-TD plane. In addition, the orientation dependent hardness and irradiation-induced hardening were confirmed. Specifically, the hardness of [001]-oriented grain is lower than that of [111]-oriented grain with and without irradiation. With the presence of irradiation, it was found that the extent of hardening is more obvious at [001]-oriented grain than [111]-oriented grain, which is attributed to a more activated primary {110} slip beneath the indenter when tested at [100]-oriented grain compared with [111]-oriented grain.