What is undercut in a weld?

What is undercut in a weld?

• A. A groove melted into the base metal at the weld toe, creating a notch that weakens the weld.
• B. A deep nipple-like projection on the weld face
• C. A slag inclusion under the weld
• D. An alignment error

Answer: (A)

Undercut is a groove melted into the base metal right at the weld toe that the weld metal fails to fill. This creates a notch along the edge and reduces the effective throat thickness of the weld, weakening the joint and making it more susceptible to cracking under load or fatigue. It often results from excessive heat input or too fast travel speed, or technique that doesn’t allow the filler metal to fully fill the joint at the toe. It’s different from a raised projection on the weld face, a slag inclusion, or an alignment error.

Undercut is a groove melted into the base metal right at the weld toe that the weld metal fails to fill. This creates a notch along the edge and reduces the effective throat thickness of the weld, weakening the joint and making it more susceptible to cracking under load or fatigue. It often results from excessive heat input or too fast travel speed, or technique that doesn’t allow the filler metal to fully fill the joint at the toe. It’s different from a raised projection on the weld face, a slag inclusion, or an alignment error.