Abstract
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.
Highlights
Hydrogen embrittlement and hydrogen-assisted cracking (HAC) are known cases of damage, mainly occurring in high-strength steels [1]
In the heat-affected zone (HAZ), bainitic and martensitic transformations result in microstructures with increased hardness and higher susceptibility for cold cracking
A positive influence on the microstructure as a result of inductive preheating could not be verified by light optical microscopy; a reduction in the hardness level in the grain coarsened heat-affected zone (GCHAZ) and the weld metal of up to 50 HV could be demonstrated exemplarily for a bead-on-plate weld on the higher-strength steel grade S460N, cf
Summary
Hydrogen embrittlement and hydrogen-assisted cracking (HAC) are known cases of damage, mainly occurring in high-strength steels [1]. For welding of higher strength steels under wet conditions, the only method globally applied by divers is the temper bead welding technique (TBW) [31,32]. This technique implies the additional deposit of functional weld beads on constructional weld beads. This challenge was recently solved by using a different induction system, which was shown to be safely applicable by divers [39,40] Still, this method needs further investigation for practical application, because heat treatment was not yet characterized for this induction system. Numerical simulations of the expected hydrogen concentration within the weld and the resulting diffusible hydrogen content after using the inductive heat treatment were conducted and validated by thermal desorption analysis
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