Residual stresses in P91 steel electron beam welds

This paper describes the characterisation of residual stress in electron beam welded P91 ferritic-martensitic steel plates (9 mm thick) by neutron diffraction and contour measurement methods. The novelty of the work lies in revealing the residual stress profile at a fine length scale associated with a similar to 1 mm wide fusion zone. A characteristic 'M' shaped distribution of stresses across the weld line is observed with high tensile peaks situated just beyond the heat affected zone/parent material boundary. Measured stresses close to the weld centreline are significantly less tensile than the adjacent peaks owing to martensitic phase transformation during cool down of the weld region. The effect of applying a second smoothing weld pass is shown to be undesirable from a residual stress standpoint because it increases the tensile magnitude and spread of residual stress. The results are suitable for validating finite element predictions of residual stress in electron beam welds made from ferritic-martensitic steels.