You could always fold your piece, forge weld it together, open it up to to where the weld is stuck, and then forge the curl wide and trim off. No rivet needed - but the best advice is already given - specially cambering the surfaces so they dont fit tight at the edges. Maybe change what you are using for a rivet, just in case they are some odd alloy. But I don't see how you can forge weld at all in a gas forge - an hour to get to welding heat? I suppose once you get your coal forge lit, and a good clean welding fire built, and the $#@* coked out of it, and a welding heat gotten to....well, it doesnt seem like it takes an hour.