Microstructure and mechanical properties of similar and dissimilar joints of RAFM and 316L by electron beam welding

Abstract

Abstract 316L is a structural material used in fusion reactor vacuum vessels (VVs), in-vessel component supports, and cooling pipes, while reduced-activation ferritic/martensitic (RAFM) steel is the structural material used in test blanket modules (TBMs). High-energy electron beam welding is a suitable method for welding RAFM/316L joints. To explore the electron beam welding process of RAFM/316L, 150 kV/39 mA are chosen as the welding parameters to connect the dissimilar materials, and the microstructure and mechanical properties of the joint are tested and analyzed after welding. The results demonstrate a magnetic deflection of the 316L/RAFM welding joint due to phase change. Thus, an electron beam shift is made to compensate for this deflection. Microstructural observations indicate that the weld metal (WM) of RAFM/316L comprises lath martensite and a small amount of ferrite. The RAFM heat-affected zone (HAZ) of RAFM/316L can be divided into three regions: a fusion zone comprising coarse ferrite and martensite, a completely quenched zone comprising quenched martensite, and an incompletely quenched zone comprising eutectic ferrite and quenched martensite. Mechanical property test results indicate that the WM of RAFM/316L is better than the 316L base material and WM of 316L/316L in terms of tensile strength, and the top of the RAFM/316L joint is comparable to, but with a weaker bottom, than that of the 316L and RAFM base materials in terms of impact toughness.