Changes of microstructure and mechanical property of the CLAM steel after long term aging at 600°C

China low activation martensitic (CLAM) steel is a new reduced activation ferritic/martensitic steel developed in China to use for blanket/first-wall structures of the D-T fusion reactor. The microstructures and mechanical properties of the CLAM steel after aging at 600°C for 1100 and 3000 h were investigated by SEM and TEM. The results showed that the prior austenite grain size did not increase with increasing aging time, while the precipitates at grain boundaries and inside grains were increased. The strength of CLAM steel was slightly increased after aging for 1100 h. When the aging time was prolonged to 3000 h, the strength of CLAM steel was decreased due to coarsening of precipitates. The ductile-brittle transition temperature (DBTT) was increased after aging for 1100 h. However, when the aging time increased to 3000 h, the DBTT lowered to the as heat-treated level. The changes of strength, toughness and DBTT after aging were interpreted from the view points of precipitation and coarsening behaviors of precipitates. It was also noticed that the low W content in the CLAM steel can effectively postpone the formation of Laves phase.