Tensile properties and microstructure of additively manufactured Grade 91 steel for nuclear applications

Laser powder bed additively manufactured Grade 91 composition steel was investigated in comparison to wrought Grade 91 steel in terms of microstructure and mechanical properties. As-deposited additively manufactured Grade 91 steel had a microstructure of lower bainitic regions surrounded by martensite. This is significantly different from the typical tempered martensitic microstructure of conventionally produced Grade 91 steel. The as-deposited additively manufactured material had excellent tensile mechanical properties with greater strength than the wrought material at room temperature, 300 and 600°C showing excellent promise for nuclear applications. Retention of strength at 300 and 600°C for the as-deposited additively manufactured material was attributed to transitional carbides in the lower bainitic regions. The additively manufactured material was also investigated in the tempered as well as normalized and tempered conditions, each showing decreased strength at elevated temperature than the as-deposited material.