RAFM Fabrication: Integrated Welding and Thermal Processing

This SBIR Phase II project will develop novel integrated welding and thermal processing methods relevant to reduced activation ferritic martensitic steels. These creep strength enhanced ferritic steels have been identified as attractive candidates for fusion reactor first wall structural materials, with compositions and properties tailored to meet reactorrelevant requirements under extremes of radiation, temperature, stress and pressure. However, weldments require post weld heat treatments to restore ductility and toughness; alternative solidstate joining processes can limit design flexibility. The focus of this work is to improve the ductility and toughness of aswelded 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 in fusion first wall structural components. Phase I testing showed feasibility of the process for reducing weld and heat affected zone hardness on commercially available modified 9Cr1Mo steels, precursors to fusionrelevant alloys. Mechanical testing demonstrated increases in weld ductility and fracture energy for integrated weld and thermal process specimens relative to baseline weld samples. Phase II tasks will involve procurement of a small heat of reduced activation ferritic martensitic steel for continued weld process development, indepth characterization, and creep coupon testing. In addition, a high temperature modified 9Cr1Mo pressure vessel prototype will be fabricated utilizing integrated welding and thermal processing, tested and destructively evaluated. Publications and outreach to the fusion materials and conventional power generation communities will assist with technology transfer and commercialization. Commercial Applications and Other Benefits: Many industries could benefit from application of integrated weld and thermal processing joining methods to enhance weld joint toughness and uniformity while reducing cost. Specific applications include creep strength enhanced ferritic martensitic steel piping, vessels and structures in petrochemical and chemical plants, conventional and nuclear fission power generation, and martensitic steels in automotive applications.