Fracture toughness properties of the heat-affected-zone in ferritic steel weldments

For safety critical applications of plant it is necessary to ensure that conservative values of mechanical properties are used for structural integrity assessments. Assessment procedures require fracture toughness often of the weldments as one of the input parameters. The main constituents of weldments are steel plate, weld metal and the heat-affected-zone (HAZ) in the plate. This paper considers the evaluation of upper shelf fracture toughness properties of HAZ. During fracture toughness testing using three point bend specimens the cracks tended to deviate from higher strength coarse grain HAZ into lower strength regions comprising weld metal or fine-grained HAZ. The tests in which cracks started in the HAZ and propagated mainly through this region yielded values of J_0.2 in the range 118MPam^1/2 to 177MPam^1/2. These experimental results are discussed with respect to the predictions of a finite element model that considers particularly the path followed by the crack within the weldment.