The radial stainless steel plates (RPs) used for Toroidal field (TF) coil in ITER are 13 m long, 9 m wide and 10 cm thick, which are quite large. Even though they are very large structures, high manufacturing tolerances and high mechanical strength at 4 K are required. It is also required that each RP should be fabricated every three weeks. Therefore, the authors intend to develop efficient manufacturing methods for ITER TF coil RP. The laser welding is then selected as a welding method for RP. Especially, the development of high technology laser welding is necessary to prevent hot cracking in the material used for the RP, namely, fully austenitic stainless steel with high nitrogen content. The authors carried out trial laser welding experiments aiming at its application to RP. As a result, it was effective to make the angle of back inclination of the weld head at the uniform welding speed. It also seemed that the sensitivity of hot cracking could be reduced by optimizing the chemical compositions of material used for RP. The base material and the welded joints satisfied mechanical properties in 4K. The application of the laser welding technology to the fully austenitic stainless steel was therefore demonstrated.
