Additive manufacturing of 316L stainless steel by electron beam melting for nuclear fusion applications
2017 (English)In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 486, 234-245 p.Article in journal (Refereed) Published
A feasibility study was performed to fabricate ITER In-Vessel components by one of the metal additive manufacturing methods, Electron Beam Melting® (EBM®). Solid specimens of SS316L with 99.8% relative density were prepared from gas atomized precursor powder granules. After the EBM® process the phase remains as austenite and the composition has practically not been changed. The RCC-MR code used for nuclear pressure vessels provides guidelines for this study and tensile tests and Charpy-V tests were carried out at 22 °C (RT) and 250 °C (ET). This work provides the first set of mechanical and microstructure data of EBM® SS316L for nuclear fusion applications. The mechanical testing shows that the yield strength, ductility and toughness are well above the acceptance criteria and only the ultimate tensile strength of EBM® SS316L is below the RCC-MR code. Microstructure characterizations reveal the presence of hierarchical structures consisting of solidified melt pools, columnar grains and irregular shaped sub-grains. Lots of precipitates enriched in Cr and Mo are observed at columnar grain boundaries while no sign of element segregation is shown at the sub-grain boundaries. Such a unique microstructure forms during a non-equilibrium process, comprising rapid solidification and a gradient ‘annealing’ process due to anisotropic thermal flow of accumulated heat inside the powder granule matrix. Relations between process parameters, specimen geometry (total building time) and sub-grain structure are discussed. Defects are formed mainly due to the large layer thickness (100 μm) which generates insufficient bonding between a few of the adjacently formed melt pools during the process. Further studies should focus on adjusting layer thickness to improve the strength of EBM® SS316L and optimizing total building time.
Place, publisher, year, edition, pages
2017. Vol. 486, 234-245 p.
316L stainless steel, Additive manufacturing, Electron beam melting, Mechanical properties, Microstructure, Nuclear fusion
Other Mechanical Engineering Metallurgy and Metallic Materials
IdentifiersURN: urn:nbn:se:miun:diva-30111DOI: 10.1016/j.jnucmat.2016.12.042ScopusID: 2-s2.0-85010310479OAI: oai:DiVA.org:miun-30111DiVA: diva2:1073974
Funding text: The project is supported by the grant F4E-GRT-516 from Fusion for Energy (F4E). This publication reflects the views only of the authors, and Fusion for Energy cannot be held responsible for any use which may be made of the information contained therein. Mechanical properties were tested by Tecnalia Research & Innovation, San Sebastian, Spain. Microstructure characterization was performed in the Electron Microscopy Centre at Stockholm University, which is supported by the Knut and Alice Wallenberg foundation. The authors would acknowledge Dr. K. Jansson and Mr. P. Jansson for their help in SEM sample preparation; Prof. T. Ekstrom for his effort in language polishing; and Mr D.Z Wang and Mr C.L Zhang in Tsinghua University for their help on EBSD characterization.2017-02-142017-02-142017-02-14Bibliographically approved