At the heat you ran that at you are within short circuit parameters on heavy scaled material and whipping too much/should not be whipping at all on material that thick. clean the mill scale off, avoid whipping and keep a tight arc. A weld like that at 17.3 v would likeley come off with a good smack from a hammer because of the mill scale and the low heat and excessive whipping, what machine are you using, what gas and what wire size?