Effect of Strength Mis-Match on Fracture Mechanical Behavior of HAZ-Notched Weld Joint.

Abstract

Strength mis-matching between the base and weld metals exerts a marked influence on the deformation behavior as well as on the fracture resistance of the weld HAZ. HAZ-notched CTOD test results for high strength steel welds were discussed with attention to mis-matching effect. Stress fields in the HAZ were addressed by 3D FEM with a model having a notch at the HAZ/weld metal boundary. Strength overmatching of the weld metal brings about different effects depending on the toughness level of the HAZ. In the case of the HAZ with moderate toughness, strength overmatching results in crack path deviation toward a softer material due to asymmetrical plastic deformation. On the other hand, for the embrittled HAZ, the overmatch condition lowers the critical CTOD value of the HAZ. This is attributed to elevation of the local stress in the HAZ by constraint effect of the overmatched weld metal. The geometry of the test specimen also affects the degree of crack tip constraint. The deep notch bend specimen produces the largest geometrical constraint. The fracture resistance of the weld HAZ is controlled by the combined effects of strength mis-matching and the specimen geometry. The geometrical constraint in the deep notch bend specimen was more significant than the constraint by 25% strength overmatching in the tension specimen.