What are slag inclusions and how do they occur?

• A. Nonmetallic slag trapped in the weld metal; occurs from incomplete slag removal, poor technique, or improper welding angle.
• B. Nonmetallic slag trapped in the weld metal; occurs from incomplete slag removal, correct technique.
• C. Porosity due to gas entrapment.
• D. Cracking due to contraction.

Answer: (A)

Slag inclusions are nonmetallic bits of slag that get trapped inside the weld metal. They happen when the slag produced during welding isn’t fully removed before the next layer is deposited, or the welder’s technique allows slag to be dragged into the weld pool. A poor technique or an improper welding angle can cause the slag to remain between passes or to be pushed into the bead, leading to these inclusions. Because the slag isn’t metallurgically bonded like the weld metal, it creates weak spots and can initiate cracks under stress. The key to preventing them is thorough slag removal between passes, along with a technique and angle that consistently pushes slag out of the joint rather than into the weld. Porosity and cracking describe different defects (gas pockets and contraction cracks) and aren’t about slag being trapped inside the weld.