Low-cycle fatigue in ultra-high-strength steel welded joints in the as-welded and post-weld-treated conditions

This study investigates four different joints under fluctuating tension cycles in the low-cycle fatigue (LCF) regime. The selected material was S960 ultra-high-strength steel, manufactured via direct-quenching manufacturing route. Based on typical engineering solutions, following were chosen to be investigated experimental tests: metal active gas and laser welded butt joints, fillet-welded load-carrying cruciform non-load-carrying double-sided transverse attachment joints. To evaluate improvement gained by post-weld treatment, both as-welded condition high-frequency mechanical impact treated from all joint types tested. In addition tests, some of analyzed using finite element (FE) models, with aim comparing accuracy assessment methods effect toe radius computational lives. results obtained tests FE analyses compared each other IIW recommendations nominal stress, structural hot-spot (HS) effective notch stress (ENS) 4R methods. results, HS are very suitable for strength LCF With method, lives remained uniformly conservative, while ENS varied depending calculation method. Using value r = 1 mm as weld rounding is justified analysis.