Microstructures and mechanical properties in two X80 weld metals produced using similar heat input

• Two welding consumables, of different chemistry, suitable to join X80 pipeline steel were studied.
• The variation in chemical composition between the wires led to differences in the microstructure and mechanical properties.
• The weld metal with higher Ti and Ni content presented finer microstructure, higher strength and lower toughness.
• The Ti inclusions helped to form a finer acicular ferrite microstructure, which generally is beneficial for toughness.
• The large number and size of Ti inclusions acted as crack initiation sites, having detrimental effect on toughness.

Two welding consumables suitable for joining X80 linepipe steel are compared in terms of weld metal microstructures, hardness, impact toughness, and tensile properties. The chemical compositions of the consumables were similar, where one of the consumables had a rich wire chemistry containing higher C, Ni, Ti alloying additions compared to a lean one. Beads on plate welding were performed using the gas metal arc welding (GMAW) process set to achieve the same heat input of 0.66 kJ/mm. The results revealed that for both wires the weld metal microstructure was mainly consist of acicular ferrite. The consumable with richer chemistry (C, Ni and Ti) exhibited higher strength and hardness due to its finer final weld metal microstructure; however, Charpy impact tests results revealed the lean chemistry wire had higher toughness at low temperature. Since both weld metals exhibited similar acicular ferrite structures, the lower toughness of the richer chemistry weld was attributed to the presence of titanium inclusions which may provide crack initiation sites.