The critical conditions of hydrogen content and residual stress in the high strength steel weld with the tensile strength level of over 980MPa were investigated. The critical hydrogen concentration for the cold cracking in the Y-grooved constraint weld joint was evaluated with intentionally introducing hydrogen gas. Residual stress conditions at the “root” portion in the weld joint were evaluated by the neutron diffraction technique. It was found that the root portion showed highest tensile stress of over 1110MPa in the transverse direction, and cracking occurred when the average hydrogen content was over 2ppm. In order to clarify the critical conditions of the principal tensile stress and local accumulated hydrogen concentration of the weld metal, the delayed fracture testing by using the notched round bar specimen with electrochemically hydrogen charged was conducted. It was seen that the cold cracking behavior in the Y-grooved weld joint was explained by the critical conditions of the maximum principal stress and the local accumulated hydrogen content obtained from the delayed fracture with the small specimen.

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