Hydrogen-assisted cracking is a major challenge in underwater wet welding of high-strength steels with a carbon equivalent larger than 0.4 wt%. In dry welding processes, post-weld heat treatment can reduce the hardness in the heat-affected zone while simultaneously lowering the diffusible hydrogen concentration in the weldment. However, common heat treatments known from atmospheric welding under dry conditions are non-applicable in the wet environment. Induction heating could make a difference since the heat is generated directly in the workpiece. In the present study, the thermal input by using a commercial induction heating system under water was characterized first. Then, the effect of an additional induction heating was examined with respect to the resulting microstructure of weldments on structural steels with different strength and composition. Moreover, the diffusible hydrogen content in weld metal was analyzed by the carrier gas hot extraction method. Post-weld induction heating could reduce the diffusible hydrogen content by −34% in 30 m simulated water depth.

Mixed connections made of normal-strength and high-strength structural steels allow for optimized material usage and production effort in applications where, as a result of different mechanical effects on materials of the same type, it would otherwise be necessary to adjust the plate thickness. Reduced material consumption and smaller weld geometries can thus generate ecological and economic advantages. When welding high-strength structural steels, however, significant softening can occur in the heat-affected zone, which can influence the load-carrying behavior of the overall joint. Since there are currently no appropriate standards for butt welds made of steels with different strengths up to S960, a separate design concept is required. In this paper, the weldability and load-carrying capacity of multilayer MAG welded butt joints designed as mixed connections of a normal-strength structural steel S355 and a high-strength structural steel in the range S690 to S960 are investigated. Extensive experimental investigations are carried out, in which other influencing variables such as the filler metal used, the heat input, the plate thickness, and the weld geometry are varied in order to identify their effects on the load-carrying capacity of the welded joints. Among other things, the results form the basis for an empirically based design model for mixed connections.

The drawn arc stud welding is widely applied in steel construction, and its welding procedure can be qualified according to different standards by visual examinations and practical destructive tests of the resulting joint. An evaluation of the material properties is usually not requested particularly considering the locally limited weld region. Nevertheless, there is a need of knowledge regarding the complex press welding process metallurgy and resulting heterogeneous material properties in the welded zone, especially when welding on base materials with specified strength and toughness behavior that might be significantly diminished. In this study, the metallurgy of standardized large low alloyed Ø20 mm steel studs welded on plates of different generic structural steel grades is comprehensively analyzed by quantitative metallography. Structural steels with a moderate nominal yield strength of 355 MPa in non-alloyed normalized and micro-alloyed thermomechanically rolled delivery condition as well as a quenched and tempered structural steel with a high nominal yield strength of 690 MPa were investigated comparatively. Despite the different base plate compositions, very similar microstructures were found in the weld metal, whereas a typical quenching microstructure that strongly depends on the steel grade occurs in the heat-affected zone. A basic suitability of all steel grades regarding the DASW metallurgy was found.

This paper deals with the analytic gap during the microstructural examination of ferritic weld metals and points out which methods can be used to perform a meaningful evaluation of the weld metal microstructure. The designers of filler materials and the respective metallographs are provided with a tool to specifically search for weaknesses in the microstructural composition and invalidate them by alloying on the basis of their metallurgical context.