Effects of tube rolling and heat treatment on microstructure and mechanical properties of CLAM rectangular tube

The first wall (FW) of China dual functional lithium lead-test blanket module (DFLL-TBM) for International Thermonuclear Experimental Reactor (ITER) contains rectangular helium flow channels, which will be fabricated by hot isostatic pressing (HIP)-diffusion welding with China low activation martensitic (CLAM) steel plates and rectangular tubes. Study on the rectangular tube fabrication process are being conducted. Rectangular tubes of 15 mm × 20 (inter dimensions of cross section) mm × 2.2 (wall thickness) mm × 1500 (length) mm were produced by hot piercing and cold rolling, and its dimensional deviation met the requirement of TBM assembly. The effects of tube rolling and heat treatment on microstructure and mechanical properties of CLAM rectangular tube were analyzed. It is found that soft annealing heat treatment after tube piercing was a suitable way to improve the ductility of the CLAM steel. The elongation should be less than 15% at every tube rolling step, and the favorable tempering temperature to release the stress caused by tube rolling was 800 °C.