Effects of carbide precipitate on the mechanical properties and irradiation behavior of the low activation martensitic steel

•Precipitates in two low activation steels were characterization using HRTEM and STEM.•The effects of the precipitates were investigated by TEM combined with tensile test.•Fine (Ta, W, V)C precipitates decreased the irradiation hardening ratio of the steel.•The interaction between precipitates and dislocation loops was discussed. Precipitates may be induced during the processing, heat treatment and reactor operating and will play a key role in determining the properties of materials. The effects of precipitates on the mechanical properties and irradiation behavior of the low activation martensitic steel have been investigated using transmission electron microscopy combined with tensile test. Two types of China low activation martensitic (CLAM) specimens (with and without Si) were chosen as the model materials. The significant microstructural difference between the two CLAM specimens was the distribution of fine (Ta, W, V) C precipitates which can strengthen materials. Nano-indentation test revealed that the fine (Ta, W, V) C precipitates promoted by adding silicon can also decrease the irradiation hardening ratio of CLAM steel because the MC precipitates with high interface-to-volume ratio could decrease the density of the dislocation loop induced during irradiation. The interaction between precipitates and irradiation induced dislocation loops was discussed.