Effect of Preheat Temperature and Microstructure on Cold Cracking in 600 MPa Grade Flux Cored Are Weld Metal

The influence of preheat and microstructure on cold cracking for high strength and low hydrogen flux cored arc (FCA) weld metal was analyzed using Y-groove test. The weld microstructure consisted of acicular ferrite and martensite. As the preheat temperature increased, the volume fraction of acicular ferrite increased and that of martensite decreased, thereby decreasing the volume expansion during the transformation from austenite to martensite. This result was consequently associated with a reduced cold cracking ratio. Cold cracking progressed mainly along the prior austenite grain boundary of martensite, and the fractograph of cold cracking consisted of intergranular fractures and quasi-cleavage fractures. With increasing the preheat temperature and decreasing the carbon equivalent, the fraction of intergranular fractures decreased and quasi-cleavage fractures increased. The microstructure related with intergranular fractures was martensite; quasi-cleavage fractures were associated with acicular ferrite.