Restraining method for delta ferrite in 9Cr-RAFM welded joint

Reduced activation ferritic/martensitic (RAFM) steels are important candidates for the first wall and blanket structure in future ADS and fission and fusion energy system. The development of welding process for fusion-centered applications is critical when evaluating the applicability of RAFM steels as structural materials for fusion pressure equipment. Delta ferrite is likely to emerge after welding owing to no nickel addition in RAFM steels, therefore, deteriorates service ability of welding structure. Restraining delta ferrite formation during welding process effectively is a key scientific and technical problem. The aim of this project is to obtain the 9Cr-RAFM steel welded joint with no delta ferrite in them. Research shows that 9Cr-RAFM welded joint can be obtained by friction stir welding without delta ferrite. The 9Cr-RAFM welded joint achieves equal matching to the base metal when the sample is just in the as welded condition. The appearance of onion rings is owing to the tungsten segregation at the interlayer. This study provides new ways to obtain the reduced activation martensite steel welded joint without delta ferrite, and also lays a theoretical foundation for the RAFM steel and the temperature controlled friction stir welding.