Abstract
For the multi-layer and multi-pass welding process of the heavy plate, the hydrogen diffusion behavior was numerically simulated to study the effect of solid-state phase transition (SSPT) on the hydrogen diffusion in the thickness direction, and the influence of the residual stress-induced diffusion after SSPT. The calculation results were compared with the experimental results. The comparison shows that the distribution of hydrogen concentration in the direction of thickness was in good agreement. The position with the most severe cold cracking sensitivity was located at a 20–30 mm depth from the top surface in this article. After welding, the hydrogen concentration in this position was kept at a high level for a long time under the effect of the size-constraint effect of the heavy plate and the existence of welding residual stress gradient. In addition, the SSPT reduced the residual stress level of weld metal (WM) significantly, increased that of the heat affected zone (HAZ), and the hydrogen was redistributed under the influence of stress. In the process of phase transformation, the parameters of hydrogen diffusion property of the material changed dramatically in a short time, the hydrogen diffusion coefficient increased in order of magnitude, and the solubility decreased in order of magnitude. This directly led to the upward diffusion of hydrogen in WM, and produced a self-gathering effect. For a welded joint of heavy plate, the self-gathering effect between passes was effective in the short-range and ineffective in the long-range.
Highlights
The hydrogen-assisted cold cracking (HACC) is one of the most common phenomenon in welded joints of high strength steel (HSS)
Weldingfield of Heavy of the molten pool, the location and size of the heat affected zone (HAZ) in the welded joint were in good agreement with
The red green and light blue areas of the molten pool, the location and size of the HAZ in the welded joint were in good agreement with showed cloud diagram inresults, the heat affected zone,8a,which solid thepart melting point
Summary
The hydrogen-assisted cold cracking (HACC) is one of the most common phenomenon in welded joints of high strength steel (HSS). HACC of welding is mainly caused by the union effect of three factors in welded joints, i.e., hardened microstructures, diffusion hydrogen enrichment, and high residual stress state. Many studies have focused on the effect of hydrogen on welded joint after welding rather than during welding. That mastering the formation mechanism of HACC is the fundamental task of controlling the cold cracking in welded joints. It is necessary to study hydrogen diffusion behavior in the micro or even smaller scale. This direction has always been concerned by the industry around the world, and many research results [1] have been achieved
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