Effects of dilution and baseplate strength on stress distributions in multipass welds deposited using low transformation temperature filler alloys

Abstract

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 multipass joints have yet to be established. This topic has been investigated by characterising the residual stress distribution in multipass welds fabricated with different welding alloys and baseplates using neutron diffraction to assess the effects of dilution and baseplate strength. While 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 baseplate. 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 multipass welded joints.

Prediction of Dilution and Its Impact on the Metallurgical and Mechanical Behavior of a Multipass Steel Weldment

“…Dilution is commonly defined as the ratio of the cross-sectional area of melted base material to the total area of the fusion zone [8], hence representing the contribution of base material to the weld metal. Therefore, for a given combination of filler and base materials, the extent of chemical heterogeneity within a weld is influenced by dilution, which can have significant effects on the metallurgical and mechanical behaviour of steel weldments [9][10][11][12]. Despite the important role that dilution plays in welding, dilution has not been considered in most published research on multipass weld modelling [13][14][15].…”

Application of low transformation-temperature filler to reduce the residual stresses in welded component

“…Special heats of phases Ci and phase transformation heat are calculated in Equations (11)(12) as functions of phase enthalpy, Hi [29]:…”

“…The effect of dilution and strength of the base metal on the residual stresses distribution in multi-pass welding using LTT fillers has been studied by Ramjavn et al [11]. They concluded that excessive lowering of Ms is not effective in reducing the tensile residual stress and creation of compressive residual stress, in addition, the residual stresses rise again for too low Ms. Also, for a greater degree of dilution and greater amounts of base metal in the fusion zone (FZ), the effect of LTT filler becomes less.…”

Solidification behaviour and microstructure of welding transition zone using low-transformation-temperature welding consumables

“…Thus, after adopting the LTT welding consumables, tensile stresses were reduced to zero, and even compressive residual stresses were generated once the transformation temperatures got lower enough [5]. In addition, the dilution has a great influence on the efficiency of LTT welding consumables [8].…”