Influence of diffusible hydrogen on brittle fracture resistibility of metal in heat-affected zone of high-strength carbon steel

摘要

Influence of diffusible hydrogen on the change of brittle fracture resistibility and mode of HAZ metal of welded joints on high-strength steels with 0,58% and 0,65% carbon content has been studied. Methods of simulation of thermal cycle of welding, saturation of model samples by hydrogen and their subsequent testing at bending were used to determine the influence of diffusible hydrogen on stress intensity factor K1C of HAZ metal. Metal microstructure in HAZ overheated zone and model sample fractures after testing were studied. It is shown that high-strength carbon steels and their joints have high susceptibility to embrittlement in the presence of hydrogen. Metal structural condition plays an essential role here. Optimum structure of HAZ metal is bainitic-martensitic one at more than 1 ratio of structural components. At saturation of joints by diffusion hydrogen occurring in welding, their brittle fracture susceptibility increases. To lower metal embrittlement, it is necessary to apply special welding processes, at which hydrogen saturation of deposited metal is minimum (less than 0,2 ml/100g) or techniques, allowing removal of diffusible hydrogen from the metal after welding.