Fatigue crack propagation of D6AC laser welds

Fatigue crack growth tests of D6AC steel plates and laser welds were performed. The effect of tempering temperatures on fatigue and mechanical properties of the material was also conducted. The results indicated that the strength of weldments was lower than that of the steel plates, with the joint efficiency of >92%. The tough structure consisted of lower bainite and tempered martensite was formed in the weld metal (WM) and the heat-affected zone, owing to a preheat of 225 degrees C were employed during welding. As a result, higher impact values and lower fatigue crack growth rates (FCGRs) of these regions were expected in the subsequent postweld heat treatments (PWHTs). In general, the FCGRs in the WM and the HAZ of laser welds were lower than those in the base metal for the same stress intensity factor range (Delta K), regardless of distinct PWHTs. The fatigue-fractured surfaces associated with them revealed transgranular and intergranular fracture modes. The zigzag nature of the crack path, particularly in the WM, could contribute to the retardation of fatigue crack propagation. Copyright (C) 1997 Elsevier Science Limited.