Microstructure, residual stress and mechanical properties of a high strength steel weld using low transformation temperature welding wires

Tensile residual stress (RS) induced by inhomogeneous temperature history and shrinkage during solidification in the welding process tends to reduce the lifetime of a welded structure. Two Cr-Ni-Mn prototype low-temperature transformation (LTT) welding wires were developed. The martensite start temperature (M-s) of the filler metal was 190 degrees C and 160 degrees C, respectively. Volume expansion associated with martensitic transformation at the relative low temperatures compensated for thermal shrinkage during solidification of the weld pool, reducing the tensile RS. High strength Q690 steel was butt welded using a conventional welding wire and the two newly developed LTT wires (LTT1 and LTT2). The corresponding RS values within the welds were measured to be 376, -311 and -513 MPa using Mathar-Soete hole drilling method. The microstructures of the welded metals with LTT1 and LTT2 wires were mainly martensitic with 3.8% and 5.1% retained austenite, respectively. The welds made with LTT wires also demonstrated higher tensile strength and hardness than the base metal and the weld with the traditional wire. (C) 2014 Elsevier Ltd. All rights reserved.