Weld Metal HACC in High Strength QT and HSLA Steel

Core Participants:
                              Australian Submarine Corporation                             
                              BlueScope Steel
                              Australian Nuclear Science and Technology Organisation
                              DSTO -Aeronautical & Maritime Research Laboratory
                              Welding Technology Institute of Australia
                              University of Wollongong
                              University of Adelaide

Project Summary:
Hydrogen-assisted cold cracking (HACC) represents a significant threat to the integrity of welded steel constructions.  The greater part of past work on understanding the mechanism of the HACC phenomenon, and on developing deterministic relationships for its minimization, has concentrated on cracking in the heat-affected zone (HAZ) of the parent metal.  In recent times, steel manufacturers have made significant progress in developing thermomechanically controlled processed steels with reduced carbon and alloy contents and this has resulted in steels that are more resistant to HACC in the HAZ.  However, improvement in the HACC resistance of the parent metal has shifted the problem of cold cracking to the weld metal. 

The benefits to industry are also significant since the defect rate is currently unpredictable and the safety of many critical structures is in question. Currently, the risk of weld metal HACC is unknown and only very conservative welding practices can be adopted. A better understanding of the phenomenon would enable safer and more economic fabrication practices to be used with increased confidence in expected service performance.


Images of a hydrogen assisted cold crack in a flux cord arc weld.  Left--image etched in Nital showing crack path.  Right--image shows the same crack on a alloy composition map (white indicates highest alloy level).