Slag Former
Slag formers are mineral additives that form a liquid slag during welding. This slag protects the melt from atmospheric oxygen and controls cooling.
Physical-chemical action mechanism
Slag formers are chemical additives that react in the molten pool and form a liquid slag. This slag forms a tight blanket over the weld metal, preventing contact with air and thus stopping oxidation. The slag can also control the cooling rate by limiting heat transfer between the melt and the surroundings.
Metallurgical relevance & welding risks
Using slag formers is crucial for a clean and defect-free weld. Without slag, the melt can quickly oxidize, leading to porosity and reduced mechanical properties. A too thick or too thin slag blanket can also cause problems: a too thick slag can coarsen the microstructure and reduce toughness, while a too thin slag doesn't provide enough protection.
Workshop practice & what to do
Choosing the right slag former depends on the alloy being welded and the desired microstructure. For steel welding, silicon or titanium are often used as slag formers. The amount is given in % of the melt mass, e.g., 0.1% silicon. It's important to remove the slag after cooling to ensure a clean and defect-free weld.