RAFM Fabrication: Integrated Welding and Thermal Processing

Reduced activation ferritic martensitic (RAFM) steels have been identified as attractive candidates for fusion reactor first wall structural materials. These chromium-rich steels have compositions and properties tailored to meet reactor-relevant requirements under extremes of radiation, temperature, stress and pressure. RAFM weldments require post weld heat treatments to restore ductility and toughness; alternative solid-state RAFM joining processes can limit design flexibility. This project will demonstrate novel integrated welding and thermal processing methods relevant to RAFM steels. A major focus of this work is to improve the ductility and toughness of as-welded RAFM steel joints without subjecting the weld to a separate post weld heat treatment, which is associated with risks of distortion and cracking. The improvements in mechanical and physical properties afforded by such a method can greatly expand the design opportunities using RAFM steels in fusion first wall structural components. Phase I will involve detailed studies on commercially available modified 9Cr-1Mo steels, the precursors to fusion RAFM steels. Integrated weld and thermal processing optimization will generate specimens for tensile, impact, weld bend ductility, hardness and microstructural evaluation, and compared to conventionally processed welds. Feasibility studies will determine suitability of implementing the processing on specific plasma facing component geometry. Outreach efforts are planned with the fusion community for validation, and to establish fabrication and testing partnerships, along with creating a detailed development plan for Phase II demonstrations on RAFM material and implementation on fusion relevant geometry. Many existing industries could benefit from application of integrated weld and thermal processing joining methods. Specific applications include martensitic steel welded tubing, vessels and structures in petrochemical and chemical plants, conventional and nuclear fission power generation, and automotive applications.