Formation mechanism and research progress of ductility dip cracking in welding of nickel-based materials

The formation and the recent research progress of ductility dip cracking（ DDC） produced during welding processes of nickel-based superalloy were summarized,several testing DDC methods and its mechanism of DDC during welding processes were discussed. The STF testing method is most suitable for the study of DDC sensitivity and was described in detail. The mechanism of the formation of ductility dip cracking,the factors affecting DDC and the ways to reduce the sensitivity of DDC were also discussed. The main ways to reduce the sensitivity of DDC are to adopt the appropriate alloying system and the appropriate welding process. The appropriate alloying system can control the grain boundary morphology,that is to say,some specific elements and C form MC carbide and are evenly distributed in the grain boundary in the form of precipitates,which will effectively pinch grain boundaries to make the grain boundaries become more tortuous,hinder the grain boundary slip and grain growth. The optimized welding technologies and heat-teartment after welding which make the grains finer can have higher resistance to DDC.