Cold Cracking Phenomenon
Cold cracking is a stress crack in the cooled microstructure, promoted by diffusing hydrogen and hardenable microstructures. This leads to crack-prone weld zones.
Physical-chemical mechanism
Cold cracking occurs when hydrogen diffuses into the metal and consolidates at grain boundaries during cooling. This creates stresses that can lead to cracks.
Metallurgical relevance & risks in welding
Cold cracking can lead to crack-prone weld zones, especially in hardenable steels like martensite. This increases the risk of hot cracking and reduces the mechanical properties of the joint.
Workshop practice & action instructions
To minimize cold cracking, the following should be done during welding:
• Use hydrogen-free shielding gases,
• Ensure slow cooling of the microstructure,
• Reduce the carbon content in the metal.
A typical target is a t8/5 time of at least 10 seconds to prevent the growth of cold cracks.