Residual Stresses in a Multi-Pass Dissimilar Metal Weld

Neutron diffraction has proven to be an excellent non-destructive technique for measurements of residual stresses in welds, in which the measured lattice plane distances are used as internal strain gauges on the level of the microstructure. However, dissimilar metal welds present added difficulties for diffraction techniques as chemistry changes within the weld region complicate the determination of a stress-free reference measurement. Another excellent residual stress measurement technique is the Contour Method, which relies on careful measurements of surface distortions on cut surfaces in combination with finite element (FE) model calculations to determine the normal residual stress component for a cut through the part, hence making it a destructive measurement technique. In the present work, time-of-flight neutron diffraction and Contour Method residual stress measurements were conducted on a model dissimilar metal weld specimen. The specimen was fabricated from a 304L stainless steel plate containing a seven pass Alloy 182 grove weld, restrained during welding and removed from the restraint for residual stress characterization. The experimental residual stress measurements are compared to the results of numerical modeling using a weld residual stress (WRS) FE model. The longitudinal stresses measured with neutron diffraction and contour method show good agreement, however, stress profiles measured parallel to the weld mid-plane with neutron diffraction tend to be broader and higher in magnitude than those measured with the Contour Method. The WRS FE model simulations using input material properties in the annealed condition effectively bound the experimental results when assuming isotropic or linear kinematic hardening behavior.