I had the same thoughts as Carburize when I was intially getting involved with this project, but as I don't have any thing else available at the moment, I am going ahead with a GMAW welding procedure to see what kind of results I can get. Otherwise, I may have to look for a different kind of filler metal. I don't think duplex will work because in the thick section we weld. We have to PWHT to for a fairly long time (couple hours)to get adequate HAZ tougness (CA6NM), and it would degrade the toughness of the filler metal (sigma and carbide precipitation). Low carbon austenitic would not meet the strength requirements. I am thinking that supermartensitic filler metal may be an option, but I don't have any experience with them on either availability or use. They seem like they could have higher toughness than the 410NiMo type. Anybody out there using these types of fillers, or think of something else that may work? I know nickel based filler might work, but that would also add significant $$$ to the project.