ABSTRACT
High strength structural steels with yield strengths of up to 1100 MPa are increasingly applied to various industrial branches for weight optimization. Recent failure cases make evident that special attention has to be paid to hydrogen assisted cold cracking avoidance in welds, if such materials are used for tubular structures, as for instance for penstocks in hydropower plants. In order to gain more insight into the cold cracking resistance of high strength steel welds, Instrumented Restraint Cracking (IRC) Tests have been performed with a S 1100 steel. As a particular item, the efficiency of various hydrogen removal heat treatments (HRHT) is currently discussed versus softening effects by annealing and an increase of the stresses and strains in the welds. For this reason, the effects of pre- and postheating on the stress-strain distribution in the root weld of a 60° V-butt joint have been investigated by finite element analyses validated by the IRC tests. Maximum transverse residual stresses at the fusion line beneath the top surface of the root weld increased with increasing restraint intensity. It turned out that preheating causes higher stresses and strains in the root weld than postheating at the same temperature and time. As a particular item, time-strain-fracture diagrams represent a very helpful tool to combine experimental and simulation results for a firm assessment of the cold cracking resistance of specific welds.
