Numerical Modelling of Cold Crack Initiation and Propagation in S 1100 QL Steel Root Welds

Although the phenomenon of Hydrogen Assisted Cold Cracking (HACC) and respective avoidance procedures have extensively been investigated in seventies and eighties, the reasons for recent failures are still a lack of knowledge about the basic hydrogen effects on steel microstructures and, in particular, a lack of welding procedure specifications and standards accounting directly and consistently for cold cracking avoidance in modern high strength structural steels with the yield strengths of up to 1100 MPa. In several previous contributions the consequences of various heat treatment procedures targeted at HACC avoidance have been shown, as for instance their effects on stress-strain build up and on hydrogen diffusion in high strength steel welds. But, the principal interaction of the three local influences on hydrogen assisted cold cracking, i.e. the local microstructure; the local mechanical load and the local hydrogen concentration have not yet been studied in detail for this type of materials. For this, a numerical model for HACC has been developed, accounting particularly for the criteria of crack initiation and propagation, like the hydrogen redistribution during the process of cracking