Microstructural Aspect of Cold Cracking in High Strength Weld Metals

摘要

Cold cracking susceptibility of multi-pass weld deposits have been known to increase with weld metal strength and diffusible hydrogen content as that of HAZ does. However, the microstructural aspect in cold cracking has not been well established. In the present study, it is demonstrated with weld metals deposited with FCAW welding wires of E71T-1 grade that weld metal cold cracks propagate following the grain boundary ferrite (GF) with an angle of 45 deg to welding direction resulting in so-called Chevron-type cracks. Based on these results, possible modifications of weld chemistry coluld be made to improve the cold crack resistance of FCA weld metals by controlling the amount of grain boundary ferrite. Following the successful results obtained, it could be confirmed that weld metal microstructure plays an important role in determining the cold cracking resistance of weld metal at the given strength. In addition, a new model relying on %GF could be suggested for estimating the preheating temperature necessary to prevent weld metal cold cracks.