Causes of ductility-dip cracks formation in in52 and in52 mss alloys during fusion welding

The aim of the paper is to investigate one of the causes of ductility-dip cracks (DDC) formation. The main aim of this work is calculation of grain boundaries (GB) cohesive energy in nickel based In52 and In52 MSS alloys. For measuring the GB energy anisotropy methods of thermal etching and light interferometry were used. DDC form on the grain boundaries of nickel based alloys due to adsorption of impurities during multipass welding. The In52 alloy has tendency to form DDC during multipass welding fusion unlike In52 MSS one doped with Mo and Nb. The main cause is the change of thermodynamic state of the GB, as it is indicated by the decrease in the cohesive energy to 1.8-1.26 J/m2. During multipass fusion welding in In52 alloy adsorption of S and O from the grains body to GB takes place. The average concentration of O and S on the surface of DDC for high angle boundaries is within 2.3-4.5 and 0.5-1 at. %, respectively. Presented in this paper results have shown the influence of welding heat for reduce the cohesive strength of GB and, as a result, of the formation of DDC. Quantitative effect of S and O as embrittlement elements on the value of decrease in the cohesive energy was shown.