Microstructure and tensile properties of laser engineered net shaped reduced activation ferritic/martensitic steel

A laser additive manufacturing technique, laser engineered net shaping (LENS), was successfully applied to manufacture a reduced activation ferritic/martensitic (RAFM) steel with nominal composition of Fe-9Cr-0.11C-1.5W-0.4Mn-0.2V-0.12Ta (wt%). The as-deposited LENS-RAFM steels were normalized and tempered. The microstructures of as-deposited and heat treated LENS-RAFM steels were characterized by using optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM). The tensile tests of as deposited and heat treated samples in different directions were carried out at room temperature and 873 K. The results showed that columnar dendrites grow epitaxially along the direction of deposition in vertical section (YOZ) and a mixture of equiaxed and columnar grains appears in horizontal section (XOY). No precipitates are observed in the as-deposited sample while Cr-rich M23C6 and Ta-rich MX type carbides appear in the heat treated sample. The as-deposited sample showed anisotropic tensile properties which could be eliminated by heat treatment. The tensile strength of the LENS-RAFM steel is similar to conventional RAFM steels such as EUROFER 97 and CLAM.