MICROSTRUCTURAL CREEP DAMAGE IN WELDED-JOINTS OF 316L STAINLESS-STEEL

The present work has been undertaken to study creep damage in welded j oints. The complex dual phase microstructure of 316L welds are simulat ed by manually filling a mould with longitudinally deposited weld bead s. Most of the moulded specimens were then aged for 2000 hours at 600 degrees C. High resolution scanning electron microscopy was extensivel y used to examine the microstructure of the welded material before and after ageing. Columnar grains of austenite constitute a matrix in whi ch thin dendrites of delta-ferrite can be found. The ageing generates the precipitation of carbides, resulting in less transformation in the material. Smooth and notched creep specimens were cut from the mould and tested at 600 degrees C under different stress levels. The creep l ife of the simulated welded material is shown to be lower than that of the base material. Microstructural observations reveal that creep cav ities are preferentially located along the austenite grain boundaries. This analysis of intergranular damage on test specimens is conducted to obtain a predictive damage law which could be used to calculate the lifetime of welded joints.