Discussion on accuracy of weld residual stress measurement by neutron diffraction; Influence of strain free reference

Suzuki, Hiroshi  ; Akita, Koichi

It is required to evaluate a strain-free reference, , to perform accurate stress measurement using neutron diffraction. In this study, accuracy of neutron stress measurement was quantitatively discussed from evaluations on a dissimilar metal butt-weld between a type 304 austenitic stainless steel and an A533B low alloy ferritic steel. In the lattice constant evaluation using a standard specimen and a sliced specimen taken from the dissimilar metal butt-weld, average lattice constant derived from multiple reflections was evaluated as the stress-free reference with cancelling out an intergranular strain, and ferrite-211 and austenite-311 reflections were judged as a suitable reflection for neutron strain measurement to reduce intergranular strain effects. Residual stress distribution in the sliced specimen evaluated using measured here exhibited higher accuracy than that measured using strain gauges. As a conclusion of this study, it was confirmed that accurate evaluation, optimization of the measurement condition, and multiple evaluations on the results play an important role to improve accuracy of the residual stress measurement using neutron diffraction.