Centerline Solidification Crack
A crystallization crack occurring along the weld centerline during the final stages of solidification due to shrinkage stresses while the material is still in a plastic state. It typically propagates longitudinally along the weld bead.
Hot cracking occurs when the weld metal is already pasty during cooling and can no longer absorb the stress. The crack then usually runs along the middle of the weld and is often only visible after grinding or etching. The problem occurs when the weld is too wide or too deep and the heat is not dissipated quickly enough. A too high sulfur or phosphorus content in the base or filler material also promotes this. In practice, this means: keep the weld not wider than necessary, do not fill too much at once, and ensure proper joint preparation. If you have the weld shape under control and dissipate heat well, this rarely happens to you. After welding, you can grind the weld and check with a crack detection agent to ensure everything is clean.