Comparative Study of Microstructure and Mechanical Properties of X80 SAW Welds Prepared Using Different Wires and Heat Inputs

The present work investigated the effect of weld composition and welding heat input on the microstructure and mechanical properties of two submerged arc welded (SAW) joints of API 5L-X80 pipeline steel. The weld metals were joined by two welding consumables (one is rich in C, Ni, Cr, Mo) under different welding heat inputs (20-22 and 34-36 kJ/cm for single-wire and triple-wire processes, respectively). The triple-wire welding procedure with less C, Ni, Cr, Mo alloy contents favors the formation of acicular ferrite (AF), whereas single-wire welding procedure with increased C, Ni, Cr, Mo contents promotes the formation of lath bainite (LB). Nanoindentation is used to evaluate the property of different microstructures. The hardness of lath bainite (LB), granular bainite (GB) and acicular ferrite (AF) is 8.0 GPa, 5.8 GPa and 3.0 GPa, respectively. The Charpy impact energy of weld metal with triple-wire welding procedure (136-165 J) is much greater than that with single-wire welding procedure (15-44 J) at − 45 °C. Larger cleavage facet size is observed in the fracture surface of single-wire weld metal. A computational procedure is developed to understand the temperature fields during the triple-wire welding. Combining the experiments and numerical simulation, simple models to predict the microstructure evolution through the weld thickness are established.