Nonmetallic residue of melted flux that floats to the top of the weld, shields it while it cools and slows its cooling. It must be removed completely with a chipping hammer, wire brush or needle scaler before the next pass, or it gets trapped as a slag inclusion. Good slag on 7018 often peels off by itself; slag that clings in the toes usually signals undercut or poor technique.
Chip all the slag out of the toes before the next pass, that's how you get wagon tracks on the film.
Also heard as
- flux residue
Related terms
Slag inclusion
Nonmetallic slag trapped inside a weld instead of floating out to the surface.
Flux
Material that shields molten metal from air and cleans oxides, as rod coating, wire core, granules or paste.
SMAW
Shielded metal arc welding: arc welding with a flux-coated consumable electrode, known in the shop as stick.
Wagon tracks
Radiographer slang for two parallel lines of slag trapped along the edges of a root pass.