Fracture toughness of CGHAZ of Q690CFD high-strength steel

The coarse grain heat affect zone (CGHAZ) of Q690CFD high-strength steel with two different compositions was simulated with Gleeble-1500 test machine to investigate its impact toughness, and the values of CTOD were measured by a series of three point bending tests. The fracture behavior of crack tip in CGHAZ was analyzed based on the fractography of CTOD samples with SEM. The results show that the variation trend of fracture toughness (critical CTOD valuesδm/c/u(8) and instrumented extension energy) declined with the decrease of temperature. The ductile-brittle transition temperature, fitted by Boltzmann function, was accordant with the variation tendency of instrumented impact. The path of crack propagation in CGHAZ of two different Q690CFD steels was determined by the position of high angle boundaries (≥15°) and M/A islands in metastructure nearby the fracture zone.