Thanks for kicking off this thread Grahame and getting this information for us.
I had attempted to weld a bit of mild rod to the end of a drill bit to give me more length. Invariably it would break at the weld and had been a futile effort. I asked a fitter machinist once what he does and he said to use Stainless Steel electrodes.....guess what.....worked a treat. It is such a nice material to weld with too. I bought a small package (10 rods, I think) just for "stock" when I need to extend a drill bit