Investigation of prior austenite grain and delta ferrite in CLAM welded joints after different diffusion annealing processes

CLAM steel is one of the structural material used in test blanket modules as a barrier or blanket for fusion reactors. Different diffusion annealing processes were employed in order to investigate the effect of δ-ferrite elimination and prior austenite grain coarsening. The results show that both alloying elements diffusion and microstructures coarsening during the diffusion annealing treatment influence the contents and morphologies of δ-ferrite. The polygonal blocky δ-ferrite and the coarse grains were determined as the main factors deteriorating the impact toughness for the CLAM welded joint. A CLAM welded joint with good impact toughness and appropriate microstructure in terms of grain size and δ-ferrite content was obtained after diffusion annealing process at 1100 °C for 10 h.