Definition - What does Cold Cracking mean?
Cold cracking is a welding discontinuity or welding defect, depending on the specification upon which the weld is being evaluated. Cold cracking causes sharp edged, narrow crevices to form intermittently or completely throughout the weld and weld heat-affected zone. Although it depends on the application, cold cracking will usually lead to complete weld failure.
Cold cracking is also called hydrogen-induced cracking or simply hydrogen cracking because hydrogen trapped in the weld and heat-affected zone is responsible for this type of cracking. This occurs when steel is rapidly cooled and allowed to form martensite. Due to the rapid cooling, hydrogen atoms trapped inside of the heat-affected zone join together and create an internal stress on the weldment. This stress, combined with a brittle microstructure like martensite, causes cracks to form.
Corrosionpedia explains Cold Cracking
Thicker materials are more prone to cold cracking because the material that is unaffected by welding serves as a heat sink, which rapidly cools the weld and allows martensite to form. Also, steels with higher amounts of carbon are more likely to experience cold cracking because the increased amount of carbon leads to an increased likelihood of martensite formation.
Cold cracking is easily prevented through a variety of methods. For cold cracking to occur there must be a susceptible microstructure such as martensite, a source of diffusible hydrogen and residual stress in the weld joint. The formation of martensite can be prevented by preheating the material being welded, thus reducing the cooling rate of the weld and heat-affected zone. Special filler materials and welding processes can be used to reduce the amount of diffusible hydrogen in the weld. Residual stress in the joint after welding can be reduced by post-weld heat treatment.