Residual stress characterization in 12%-Cr steel friction stir welds by neutron diffraction

In the present paper we report the results of a study into friction stir welds made in 12.7 mm-thick 12%-Cr steel plates. Residual stress measurements were performed using angle-dispersive neutron diffraction. Complete characterization of the three-dimensional residual stress state in friction stir weld samples was obtained by analysing diffracted peaks; peak broadening for identifying the regions of severe plastic deformation and the associated residual strain (eigenstrain) acting as the source of residual stress and peak shifting for evaluating residual elastic strains in the welded component. Three different methods were used to address the key issue of determining the do variation across the weld. The comb (or matchstick) method was compared with two other approaches: the balance method, and the zero traction method. It was found that a combination of the comb and the zero traction methods allows reliable residual strain/stress distributions.