Effect of Process Variables on Weld MetalHydrogen-Assisted Cold Cracking in Multipass Welds of High Strength Steels

The current trend to reduce CO2 emissions and improve energy efficiency has brought about increased usage of lean composition, high strength steels, with yield strength between 690MPa - 1100MPa. These steels necessitate the use of highly alloyed, comparable strength, welding consumables, which has led to an increase in prevalence of weld metal cracking. So far industrial techniques for avoidance of hydrogen-assisted cold cracking are still focused on heat affected zone cracking. Therefore, a need has arisen to define the mechanism of weld metal hydrogen-assisted cold cracking and offer procedural parameters specific to the avoidance of weld metal hydrogen-assisted cold cracking. This study investigates weld metal hydrogen-assisted cold cracking in a systematic engineering way, including a review of current industrial practice, cracking mechanism and morphology, cracking susceptibility, and the factors that contribute to cracking, and their measurement and control. Further investigation includes hydrogen behaviour during welding and hydrogen-steel microstructural interactions. Conditions resulting in cracking in weld metal are established and process variables are tested to evaluate their effectiveness to reduce weld metal cracking. The findings show that preheating is the most effective procedural parameter for reducing susceptibility to weld metal hydrogen-assisted cold cracking. Additionally, this work confirms that British Standard (BSI, 2001) specified for the avoidance of heat affected zone hydrogen-assisted cold cracking is effective for avoiding weld metal cracking. Furthermore, if this standard is not followed then cracking susceptibility will increase in the heat affected zone and weld metal, therefore it is important to ensure that post weld non-destructive testing techniques are effective at detecting cracking in both regions.