Submerged arc welding buries the arc under a blanket of granular flux, which shields the weld from the atmosphere and allows very high deposition rates with no visible arc, no spatter and no fume. It is the process behind most heavy structural steel, pressure vessels, pipe and large shafts.
The wire is bare and solid, typically 3/32 to 1/8 in, and the flux is fed separately and recovered for reuse. Because the arc runs under flux, the process is limited to flat and horizontal positions — it cannot be used out of position.
Wire and flux are matched as a combination, and the classification (such as F7A2-EM12K) describes the deposit properties of that wire-flux pair. Changing either component changes the mechanical properties of the weld, so the pair must be treated as a single consumable.
High deposition rates mean high heat input, which affects the toughness of the heat-affected zone. On thick sections this drives the need for preheat, interpass temperature control and sometimes post-weld heat treatment.
