Microstructural development in advanced ferritic-martensitic steel HCM12A

HCM12A is an advanced nominal 12Cr ferritic-martensitic steel designed for higher temperature operation and is under consideration for application in core components in Generation IV nuclear energy systems. This work provides information on the hardening and microstructural changes in HCM12A after irradiation using 2.0 MeV protons at 400 °C to 10 dpa and at 500 °C to 3 dpa, and using 5 MeV Ni-ions at 500 °C to 50 dpa. Following irradiation, changes in hardness were measured using Vickers hardness indentation, changes in microstructure and phase stability were studied using transmission electron microscopy, and changes in microchemistry were measured using scanning Auger microscopy and analytical electron microscopy. The hardness at 400 °C increases by roughly 70% and saturates by roughly 5 dpa. The microstructural changes contributing to this hardness increase are mainly the formation of precipitate phases. Hardness increases are much smaller at 500 °C. Chromium is enriched at grain boundaries prior to irradiation, likely due to grain boundary carbides, and increases further during irradiation at least partially due to radiation-induced segregation.