Review: Low transformation temperature weld filler for tensile residual stress reduction

• A review of low transformation temperature (LTT) weld filler alloy concepts.
• The latest theory and practice for the design of LTT weld filler are discussed.
• The technique has been shown to increase fatigue strength.
• The technique may enable engineering design codes to be favourably re-drafted.

An attractive, alternative approach for the reduction of harmful residual stresses in weld zones is reviewed, which utilises low temperature, solid-state, displacive phase transformations in steel. The theory, latest concepts and practice for the design of such low transformation temperature (LTT) filler alloys are considered. By engineering the phase transformation temperature of the weld metal so as to take advantage of transformation expansion, the residual stress state within the weld zone can be significantly altered, most particularly where the weld thermally contracts with any movement of base parts constrained. To date, the technique has been shown to increase fatigue strength for some common weld geometries, which may enable engineering design codes to be favourably re-drafted where such LTT filler alloys are used.