Transformation plasticity can be utilised to control residual stresses in steel welds. This requires special filler alloys that transform at a sufficiently low temperature to compensate for accumulated thermal contraction strains. However, the welding parameters needed to optimise the effect in multi-pass joints have yet to be established. This topic has been investigated by characterising the residual stress distribution in multi-pass welds fabricated with different welding alloys and base plates using neutron diffraction to assess the effects of dilution and base plate strength. Whilst the use of richly-alloyed weld metal does enhance fatigue performance in single-pass joints, the extent of stress relief that can be derived from transformation plasticity is reduced due to incomplete martensitic transformation when further layers are deposited. For all cases studied, compressive stresses were measured in the weld metal with balancing tensile stress in the heat-affected zone of the plate. The magnitude of the tension was observed to be a function of the strength of the base plate. Recommendations are also presented for the combination of welding and material parameters that lead to the optimum exploitation of transformation plasticity as a method for boosting the fatigue performance of multi-pass welded joints.
Science and Technology of Welding and Joining 19 (2014) 461-467.
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