In arc-welding, what do we call the melting chemicals that create a protective barrier for the weld?

In the context of arc-welding, the melting chemicals that create a protective barrier for the weld are known as slag. Slag is formed when flux materials and other compounds melt and solidify over the molten weld pool. Its primary purpose is to protect the weld from atmospheric contamination such as oxygen and nitrogen, which can lead to defects and weaken the weld quality.

By providing this protective layer, slag helps to ensure a cleaner and stronger weld joint. After the welding process is complete, the slag can be chipped away to reveal a solidified and well-formed bead. This protective function is critical in maintaining the integrity of the weld, particularly in environments where exposure to air could compromise the weld.

While flux is also used in welding to cleanse the base metal and facilitate fusion, it is the slag that specifically refers to the solidified by-product that occurs during the welding process. Filler material pertains to additional material that is added to the weld pool to help create the joint but doesn't refer to the protective layer. Solder is a different material altogether, used in joining metals at a lower melting point, typically in electrical and plumbing applications.