What are crater cracks in GMAW and how can they be prevented?

• A. Crater cracks are cracks in filler wire; prevent by using larger wire.
• B. Crater cracks occur at weld root during cooling; prevent by increasing travel speed.
• C. Crater cracks occur in shielding gas; prevent by increasing gas flow.
• D. Crater cracks occur at the end of a weld due to thermal contraction; prevent by filling the crater with additional bead or short weave before ending and by controlling cooling.

Answer: (D)

Crater cracks form at the end of a GMAW weld as the last deposited metal cools and contracts, creating tensile stresses in that area. If the crater is left open, this stress concentration can initiate a crack that propagates into the weld. The best way to prevent this is to finish the crater properly by adding material with a short final bead or a light weave to close the crater before stopping. This smooths the transition as it solidifies and reduces the stress concentration that leads to cracking. Controlling cooling is also important—keep a steady heat input, avoid an abrupt stop, and consider adjustments to technique or preheating if needed to prevent rapid cooling that can exacerbate contraction cracks. In short, avoid ending the weld with an open crater and manage how quickly the metal cools.