Hydrogen Charging of High Strength Steel Specimens and Physical Simulation of Cold Cracking under Laser Beam Welding Conditions

Cold cracks occur during the cooling down of welded joint at low temperatures or later at room temperature after the end of welding. It is associated with the formation of brittle microstructures as martensite in the presence of diffusible hydrogen as well as of tension stresses. By using an enhanced Simulation- und Testing Center Gleeble 3500, a procedure for physical simulation of cold cracking under laser beam welding conditions is suggested. The approach reproduces combinations of the cold crack main parameters, a brittle microstructure, tension stress and high local hydrogen concentration under welding conditions which induce a cold crack. A specimen geometry and technique were developed to enable the gaseous hydrogen charging from pure hydrogen atmosphere. The amount of charged hydrogen can be adjusted through varying the charging parameters like temperature, gas pressure and charging time. The hydrogen charging technique and the cold crack testing procedure were proven with high strength steel specimens.