Abstract
Shielded metal arc (SMA), gas tungsten arc (GTA), and wide-gap tungsten arc weldments were produced to study the influence of welding process on fatigue crack growth behavior of 308L austenitic stainless steel weldments at room temperature (RT) and 288 °C. Both SMA and GTA weldments showed dendritic microstructure with FA solidification mode; however, the lower heat input with larger (Cr/Ni)eq in SMAW process led to lathy ferrite morphology and more residual ferrite in the SMA welds, while vermicular ferrite morphology was shown in GTA weldments. The yield strength of the welds significantly increased with the decreasing elongation, which was mainly due to the dual phase strengthening effect after rapid solidification during welding. All the weldments showed better fatigue resistance than the 304L base metal at RT and 288 °C in air, which was attributed to the non-homogeneous structure leading to a rougher and more complex crack path. In addition, no strengthening effect by deformation-induced martensitic transformation was observed in both welds. Moreover, due to the slower welding speed in the first pass on the wide-gap GTA weldment, larger spacing dendritic structure was produced along the welding direction at the center, which led to higher fatigue crack growth rate (FCGR) than that of SMA and GTA welds at lower ∆K region; however, the FCGR of all welds converged as ∆K reached 32 and above. The influence of microstructure on the FCGR was more distinct at lower ∆K region, which could be observed only on specimens without side-grooves, where crack growth direction was not limited, and then the crack growth behavior switched to stress-state controlled mode where the plastic zone became sufficiently large and the fracture surface displayed more ridges and quasi-cleavage fracture.