Effect of N on the precipitation behaviours of the reduced activation ferritic/martensitic steel CLF-1 after thermal ageing

In this work, thermal ageing of the reduced activation ferritic/martensitic steel CLF-1 with a nitrogen content of 0.025% has been performed at temperatures of 823 K and 873 K for 6000 h. Mechanical properties (hardness, tensile and Charpy impact) and microstructure characterisation has been carried out. After thermal ageing treatments, the steels showed similar values of hardness and tensile properties and a slight deterioration of impact properties were observed. After long term thermal ageing, the M23C6-type precipitation coarsens and agglomerates along lath and grain boundaries. Compared with steels that have lower nitrogen content, the coarsening and agglomeration of M23C6 in the steels with higher nitrogen content is much lower and the steel shows higher microstructural stability.