Residual stresses in P91 steel electron beam welds

Abstract

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 ∼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.

Keywords:

• Ferritic–martensitic steel
• Neutron diffraction
• Phase transformation
• Type IV cracking

The research was supported by the Indian Department of Atomic Energy and by grant EP/101215X/1 from the UK Engineering and Physical Research Council. The authors gratefully acknowledge the award of neutron beamtime by the UK STFC, the contributions of Mr Majid Ali and Mr S. N. Nagchi who carried out the electron beam welding and Dr Foroogh Hosseinzadeh who supported the contour residual stress measurements.