Effect of Residual Stress on Hydrogen Diffusion in Flat Butt Welding Joints

Abstract

Flat butt welding is commonly used to construct large welded structures, such as ships. Under high temperatures during the welding process, the hydrogen-containing compound in the arc welding decomposes into monoatomic hydrogen, which is dissolved in the molten pool in large amounts. High-strength steel, widely used for large ship structures, is sensitive to welding residual stress. Non-uniform welding residual stresses in such structures could facilitate the diffusion and accumulation of hydrogen in the steel, leading to excessive hydrogen localized at the welded joints. This behavior can cause hydrogen embrittlement, threatening the safety and reliability of ship structures. In this study, based on the thermal elastic-plastic theory and the theory of residual stress-induced hydrogen diffusion, a three-dimensional finite element analysis thermodynamic model for the flat butt welding joints of high-strength steel was established, the welding process was simulated, and the distribution law for the welding residual stress field was obtained. Then the sequential coupling calculation of hydrogen diffusion was performed by defining the welding residual stress field of flat butt welding joint of high strength steel as the pre-defined field, and the hydrogen diffusion behavior under the welding residual stress field was obtained. The results revealed large residual stresses in the weld and heat-affected zone of the butt welded joints of high-strength steel plates. As the distance from the weld increased, the level of welding residual stress decreased rapidly. The welding residual stress affected the hydrogen diffusion behavior, and hydrogen was enriched in regions with high residual stress. Moreover, hydrogen-induced cracking occurred easily in the weld and heat-affected zone. These results can provide theoretical support for ensuring the safety and reliability of large ship structures.