Thermal modelling of steel welds
Thesis DisciplineMechanical Engineering
Degree GrantorUniversity of Canterbury
Degree NameMaster of Engineering
The metal adjacent to a weld is exposed to severe thermal events. As a result, complex changes in metallurgical structure occur in this region. By varying certain welding parameters, the weld joint strength can be optimized. Two conditions necessary for hydrogen (cold) cracking of welds to occur are a susceptible microstructure (i.e. hard), and the presence of sufficient diffusible hydrogen. Both of these conditions are strongly influenced by how the weld cools. A finite element model was developed, suitable for predicting the thermal history of welds. The model incorporates temperature dependent thermal properties and latent heats. Arc energy is added as a heat flux density over a double ellipsoidal model of the weld pool. The model was used to obtain heat affected zone cooling times, allowing prediction of hydrogen cracking susceptibility. The predictions were verified with previous finite element and experimental studies. A parametric analysis was performed to find the influence of a number of weld conditions on cooling behaviour. Initial results from three-dimensional models indicated the relative safety, from cracking, of welded bar joints compared to plate joints.