Improvement of the mechanical properties of wet underwater fillet welds on high-strength steels

In a research project, welding tests were carried out by experienced underwater welders under real conditions and then mechanically tested. The aim was to determine and evaluate the mechanical properties and to assess the partial safety and correlation coefficients used for the structural design in accordance with standard DIN EN 1993-1-8. For this purpose, the maximum permissible stress was calculated using the coefficients specified in the standard and these were compared with the maximum load-bearing capacity of the joints determined. It was possible to show that the stresses borne by the samples are above the minimum strength and that the partial safety and correlation coefficients can therefore also be used for welds on the tested high-strength sheet pile steel S430 GP. In addition, the inductive post-weld heat treatment of weld seams under water was investigated. For this purpose, fillet welds were welded under laboratory conditions using a gravity-driven welding device. Selected weld seams were then subjected to inductive post-weld heat treatment. Two post-weld heat treatment strategies were used: heating up to the AC1-temperature and above the AC3-temperature. It was observed that the hardness and hydrogen content could be reduced and the strength of the joint increased with the help of inductive post-heat treatment. In addition, differences in the influences of the two post-heating strategies investigated were identified.