Cold cracking (metallurgy)

Cold cracking names a metallurgical mechanism, not merely a crack that feels cold when found. It develops after solidification and cooling, often in a hardened heat-affected zone or in susceptible weld metal. Diffusible hydrogen supplies the embrittling influence, the local microstructure supplies a vulnerable path, and tensile residual stress supplies the driving force. Removing one part of that combination changes the risk; finding a crack does not identify which control failed.

ISO 17642-1 covers the fundamentals and general principles of cold-cracking tests for arc-welded metallic materials. Its scope is susceptibility testing of consumables, parent materials and weld metal. It does not provide an acceptance decision for a production weld. The applicable construction specification and inspection procedure remain the places to look up examination timing and disposition.

Worked distinction: cold cracking and hot cracking

Imagine a restrained steel qualification coupon that looks sound when welding ends. The next day, inspection finds a narrow crack beside the fusion boundary in a hard region. Review also finds an uncontrolled hydrogen source. That sequence supports a cold-cracking investigation: the fracture appeared after cooling in the combination described above.

If a centreline crack instead opens as the pool finishes solidifying, the timing and location point to hot cracking, whose test family is ISO 17641-1. Calling both findings simply “weld cracks” hides the different mechanisms and sends corrective work in the wrong direction. Hydrogen cracking is the closest neighbour term and, for the steel-welding mechanism described here, usually another name for cold cracking; hot cracking is a different mechanism.

Records of preheat temperature, consumable condition and joint restraint help reconstruct exposure. They do not establish that a crack exists. That finding still comes from the examination route specified for the job.