Fatigue strength prediction of ultra high strength steel butt-welded joints

摘要

First, fatigue tests were performed on butt-welded joints made of novel direct quenched ultra high strength steel with high quality welds. Two different welding processes were used: MAG and Pulsed MAG. The weld profiles, misalignments and residual stresses were measured, and the material properties of the heat-affected zone were determined. Fatigue tests were carried out with constant amplitude tensile loading both for joints in as-welded condition and for joints after ultrasonic peening treatment. Finally, in fatigue strength predictions, the crack initiation phase was estimated using the procedures described by Lawrence et al. [Lawrence F V, Ho N J and Mazumdar P K (1981) Predicting the fatigue resistance of welds. Annu. Rev. Mater. Sci, 11, 401-425]. The propagation phase was simply estimated using S-N curves for normal quality butt welds, which may contain pre-existing cracks or crack-like defects eliminating the crack initiation stage.