I wouldn't hessitate to weld it. However, I wouldn't even bother trying to see how it works without re heat treating it first. It's not a big deal to do, easier that the welding and shaping of the nib. Since the material is unknown, I would bring it up to critical (non magnetic) then quench in room temp water with 1/4" of ATF floating on top then temper in molten lead. Put the sping on top of the lead then apply the heat. Once the lead melts, hold the spring under the surface for a few minutes then remove the heat. Lead melts @ 620degF and 620 to perhaps 650 is a good temp for tempering many spring steels, the lead, of course CAN get alot hotter if allowed. So, remove the heat and let it solidify with the spring under the surface. Then reapply the heat and when the spring pops to the top take it out and your done. I like to smoke the spring over a kerosene lamp before putting it into the lead. This prevents the lead from sticking to the spring. Best case scenario, you have a spring as good as the original with very little effort. Worst case scenario, the spring fails and you have to make a new one from scratch. Not a big deal either.
