What causes crater cracks and how can they be prevented?
What will be an ideal response?
Crater cracks are the tiny cracks that develop in the weld craters as the weld pool shrinks and solidifies. Materials with a low melting temperature are rejected toward the crater center while freezing. Since these materials are the last to freeze, they are pulled apart or separated, as a result of the weld metal's shrinking as it cools. The high shrinkage stresses aggravate crack formation. Crater cracks can be minimized, if not prevented, by not interrupting the arc quickly at the end of a weld. This allows the arc to lengthen, the current to drop gradually, and the crater to fill and cool more slowly. Some GMAW equipment has a crater filling control that automatically and gradually reduces the wire feed speed at the end of a weld. For all other welding processes the most effective way of preventing crater cracking is to slightly pull the weld back allowing it to pool up on the weld bead before breaking the arc.
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