Fracture behavior of simulated heat affected zones in S690QL high strength steel

The fracture mechanics characterisation of different locations in the heat-affected zone (HAZ) is not possible due to steep gradients and large variability. The Gleeble thermo-mechanical simulations, can reproduce the characteristic HAZ microstructures, in a volume convenient for testing. In this study, the GMAW welding thermal cycles are simulated on High Strength Steel (HSS) S690QL specimens. To reproduce two-pass welding HAZ microstructures, two consecutive thermal cycles are physically simulated. Testing of tensile properties, ASTM E1820 fracture toughness and ASTM E647 fatigue crack growth is done. Tensile tests show that the increase of reheat temperatures in 2 nd cycle leads to strength decrease. The J IC fracture toughness and Stress intensity factor (SIF) K JIC values are highest for CGHAZ region, being reheated to 1250 °C in 2 nd welding cycle. Fatigue crack growth rate tests were performed for each characteristic HAZ microstructure. The CGHAZ zone has the lowest resistance to fatigue crack growth.