You need to ditch the flux core and get yourself a small bottle of Argon/ Co2, 25/75, possibly called Stargon . . to shield your welds.
Talk with your welding supplier to get the right gas for what you are doing. Different gas mixes burn at different temperatures, some are designed for dirty lightly rusted steel, others for clean steel. Get the right gas, use the right heat setting on the welder.
Then you aren't dealing with all that slag getting into your bead. Fulx core is for welding old plow shares.
Welding Technique consists of the 4 key points of welding:
