Influence of different microstructures of the welding zone on the fatigue crack growth behaviour of HSLA steels

摘要

To meet the cost and weight reduction requirements in welded structures,high-strength low-alloy (HSLA) steels are increasingly used in all fields of mechanical engineering.However,in comparison to low-strength steels these materials are more susceptible to notches or initial cracks.Therefore,an extensive investigation of fatigue crack growth behaviour in the different microstructural zones of the heat-affected zone (HAZ) of the weld is necessary for an appropriate lifetime evaluation of welded joints.For this purpose,fracture mechanics parameters like thresholds and crack growth rates in the different microstructural zones of the HAZ as well as in the base material are characterized by single edge notched bending (SENB) specimens.The different microstructures are reproduced with a Gleeble thermal simulator system using the same heating curves as measured previously during the welding process of a representative joint.The specimens feature the three characteristic microstructural zones of the HAZ (intercritical,fine-grained and coarse-grained zone).The effect of varying stress ratio R on the crack growth threshold and the crack growth curves is also assessed.