Influence of Temperature on Tearing Resistance of Welds for PWR Vessels

The effect of temp. on ductile fracture toughness of three narrow gap SAW welds and one MMAW weld (SA 508 Cl.3 base metal) was investigated using 25 mm thick CT specimens. Chemical analyses, tensile and Charpy V tests were also performed. Two methods of toughness characterization (partial unloadings or interrupted tests) were used at 20-43 deg C and service temp. (293 deg C). Values of J at initiation, and after a moderate propagation were considered and compared. At a given temp., properties of the four welds were fairly similar. A conservative estimate of the toughness reduction factor, associated with a temp. increase from 43-293 deg C, is J exp 293 approx = J exp 43 /1.6. Fracture surfaces were examined, showing a pattern of patches with dimples separated by areas of smoother surfaces. This fracture surface appearance can be related to the weld microstructure. Two models were tried for predicting the change of fracture toughness with temp. through the effect of this latter parameter on tensile properties. The characteristic distance model of ductile fracture provides a satisfactory estimate of the temp. effect on toughness. 10 ref.--AA