What is slag in welding?

Slag is a byproduct of the welding process that is formed when the flux coating on the welding electrode melts and forms a protective layer over the weld pool. This layer helps to protect the molten metal from atmospheric contamination, and also helps to shape and control the weld bead.

Slag must be removed from the weld after it has solidified, as it can trap impurities and weaken the weld. It is typically removed using a chipping hammer or wire brush, and should be removed before beginning any further welding on the workpiece.

In some welding processes, such as shielded metal arc welding (SMAW), the slag can be easily removed by simply striking it with the welding electrode. In other processes, such as gas metal arc welding (GMAW) or flux-cored arc welding (FCAW), the slag must be manually removed with a chipper or wire brush.

It is important to remove all of the slag from the weld before proceeding with any further welding or finishing operations, as any remaining slag can lead to defects in the finished weld.