HAZ Properties in HPS Solid State Welds

High Performance Steels having up to 100 ksi yield strength, good toughness, weldability, and weathering characteristics could be used in arctic environments in structural and tubular applications. At the same time, the A1010 structural ferritic stainless steel with 12%Cr has also been promoted because of its good corrosion resistance in associated welded structures. This work deals with solid-state welding of these steels using High-Frequency Enhanced- and traditional Friction Stir Welding, and the novel Thermal Stir Welding process, when compared with fusion welding.

Following process modeling and Design of Experiments that included heat input normalization, solid-state welds were performed at different labs, followed by non-destructive and destructive testing of the full-penetration one-sided welds in 0.25” thick base metal butt-joints. Reference SMAW, SAW and GMAW/FCAW fusion-weld database was established for the same thickness and joint geometry.

It was found that solid-state welds had superior HAZ toughness in all solid-state welds, when compared to fusion welds. It was found also that for dissimilar combinations of HPS and A1010, the solid-state welding processes produced a better transition in properties across the welds. However, formation of intermetallics, voids and other inclusions in all stir-based processes required parameter optimization, as well as in-line Post Weld Heat Treatment. The lower welding speed, tool wear and wide HAZ remained the main disadvantages of solid-state welding and more work is needed to optimize them in the future.

It was concluded that although solid-state welds showed improved HAZ toughness when compared with fusion welds, there were significant differences in weld zone properties, productivity and overall estimated cost/implementation potential of the solid-state welding. While fusion welding will likely remain the most economical and flexible welding method in joining steels in arctic environments, it is believed that there will be specific applications for each of the steels and solid-state welding process examined.