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Revealing microstructure characteristics and mechanical properties of directly tempered a newly developed RAFM steel fabricated by laser powder bed fusion.

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Title: Revealing microstructure characteristics and mechanical properties of directly tempered a newly developed RAFM steel fabricated by laser powder bed fusion.
Authors: Liang, Xin1 (AUTHOR), Chai, Linjiang1 (AUTHOR) chailinjiang@cqut.edu.cn, Li, Jincheng1 (AUTHOR), Wang, Zhichen1 (AUTHOR), Yang, Yimeng1 (AUTHOR), Niu, Ying1 (AUTHOR), Zhao, Xiaotong1 (AUTHOR), Wu, Yu1,2 (AUTHOR) abrahamwy@126.com, Tan, Xiaolian2 (AUTHOR)
Source: Materials Science & Engineering: A. Jul2026, Vol. 965, pN.PAG-N.PAG. 1p.
Subjects: Microstructure, Tempering, Powder bed fusion, Ferritic steel, Tensile strength, Mechanical behavior of materials, Carbides
Abstract: Reduced activation ferritic-martensitic (RAFM) steel, owing to its excellent in-reactor performance, is regarded as one of the most promising candidate structural materials for future advanced reactors. Given the structural complexity of specific in-reactor components, additive manufacturing technologies with near-net-shape capabilities have been increasingly applied to the fabrication of RAFM steel. In this work, a cylindrical component of newly developed RAFM steel was fabricated using laser powder bed fusion (LPBF) and subsequently subjected to direct tempering at 700-800 °C. Multiple characterization techniques were jointly employed to analyze the microstructures and mechanical properties before and after the heat treatments, thereby elucidating how specific microstructural features affect the material's tensile strength and hardness. The as-printed microstructure is comprised of fine martensitic laths with a high dislocation density, coarse blocky ferrite and a small amount of retained austenite, along with a few dispersed precipitate particles (Cr 23 C 6 and (Ta, V)C). After tempering, the retained austenite disappears, the dislocation density considerably decreases, and many carbides appear along ferritic grain and martensitic lath boundaries. The as-printed specimen exhibits a tensile strength of 1331.1 MPa and an elongation of 12.8%, demonstrating favorable strength-ductility balance; after tempering, the tensile strength decreases with the ductility essentially maintained. Analyses reveal that the superior strength of the LPBFed specimen jointly originates from grain boundary strengthening, dislocation strengthening, solid-solution strengthening, and hetero-deformation strengthening induced by structural heterogeneity; after tempering, the strength reduction primarily results from weakened dislocation and solid-solution strengthening because of the decreased dislocation density and the precipitation of solute elements. [ABSTRACT FROM AUTHOR]
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Database: Engineering Source
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Abstract:Reduced activation ferritic-martensitic (RAFM) steel, owing to its excellent in-reactor performance, is regarded as one of the most promising candidate structural materials for future advanced reactors. Given the structural complexity of specific in-reactor components, additive manufacturing technologies with near-net-shape capabilities have been increasingly applied to the fabrication of RAFM steel. In this work, a cylindrical component of newly developed RAFM steel was fabricated using laser powder bed fusion (LPBF) and subsequently subjected to direct tempering at 700-800 °C. Multiple characterization techniques were jointly employed to analyze the microstructures and mechanical properties before and after the heat treatments, thereby elucidating how specific microstructural features affect the material's tensile strength and hardness. The as-printed microstructure is comprised of fine martensitic laths with a high dislocation density, coarse blocky ferrite and a small amount of retained austenite, along with a few dispersed precipitate particles (Cr 23 C 6 and (Ta, V)C). After tempering, the retained austenite disappears, the dislocation density considerably decreases, and many carbides appear along ferritic grain and martensitic lath boundaries. The as-printed specimen exhibits a tensile strength of 1331.1 MPa and an elongation of 12.8%, demonstrating favorable strength-ductility balance; after tempering, the tensile strength decreases with the ductility essentially maintained. Analyses reveal that the superior strength of the LPBFed specimen jointly originates from grain boundary strengthening, dislocation strengthening, solid-solution strengthening, and hetero-deformation strengthening induced by structural heterogeneity; after tempering, the strength reduction primarily results from weakened dislocation and solid-solution strengthening because of the decreased dislocation density and the precipitation of solute elements. [ABSTRACT FROM AUTHOR]
ISSN:09215093
DOI:10.1016/j.msea.2026.150315