応力分布および拡散性水素濃度分布を考慮した局所限界条件に基づく高強度鋼溶接金属の低温割れ発生特性に関する検討

抄録

Hydrogen-induced cold cracking of welds needs to be solved to promote the application of high-strength steel. Cold cracking has been investigated through slit-type weld cracking tests. These tests afford appropriate conditions to avoid cold cracking in terms of factors such as chemical composition, hydrogen concentration, welding conditions, plate thickness, and groove geometry. However, the process of cold cracking of welds should be based on more microscopic criteria, because stress concentration and diffusible hydrogen accumulation are the governing processes of cold cracking on a microscopic scale.
In this study, cold cracking of a high-strength steel weld metal was evaluated by considering local stress and locally accumulated hydrogen concentration. First, a limit condition for the high-strength steel weld metal was determined through a series of slow strain rate tensile tests. Finite element simulation of stress distribution and hydrogen concentration distribution were performed to determine the limit condition of cold cracking using local stress and locally accumulated hydrogen concentration. Second, finite element simulations of weld-induced stress and hydrogen diffusion in the Y-groove weld cracking test specimen were performed. The histories of local stress and locally accumulated hydrogen concentration at the weld root were calculated under various initial diffusible hydrogen concentrations. When the initial diffusible hydrogen concentration was higher than a certain value, the local stress and locally accumulated hydrogen concentration at the weld root could exceed the cold cracking limit. Whether cold cracking occurred or not was agreed with the experimental results.