Microstructural Approach on Cold Cracking for High Strength FCA Steel Welds of YS 600 MPa Grade

摘要

Cold cracking is observed at HAZ and weld metal at temperatures below 200°C. It is caused by the interaction of susceptible microstructures, diffusible hydrogen, and tensile residual stress in welds. To minimize cold cracking, preheating and/or post-heating processes need to be applied for welding. Steel plates for the ocean plants are normally welded by using flux-cored arc (FCA) to maximize weld productivity. However, FCA-weld metals are more sensitive to cold cracking compared to solid wire because of their large moisture adsorption. The increased use of high strength steels with yield strengths (YS) greater than 600 MPa has also changed the weld microstructure from a mixture of proeutectoid ferrite and acicular ferrite to bainite and martensite. However, there were only few studies on the effect of preheating temperature on microstructure and cold cracking properties in high strength steel welds. This study investigated the role of weld metal composition and preheating temperature on the cold cracking of welds deposited with YS 600 MPa and low-hydrogen FCA weld consumables. Cold cracking fractography and crack propagation behavior were analyzed to investigate the relationship between cold cracking and microstructure in the high strength steel welds.