Corrosion of simulated weld HAZ of API X-80 pipeline steel

Four peak temperatures and two cooling rates were used in a Gleeble thermomechanical processing machine to simulate weld HAZ of API X-80 pipeline steel. Bainitic microstructures were observed at both 30 and 100 °C/s cooling rates. Bainite favoured higher passive current densities in alkaline solutions. The lowest peak temperature, 770 °C, produced the highest martensite-retained austenite (M–A) phase in the microstructure. Presence of M–A phases in the microstructure extended the passive region to higher potentials in alkaline solutions. Corrosion current density of the as-received sample was higher in acidic solutions and lower in alkaline solutions compared to the heat-treated ones.

► Corrosion of the heat affected zone of API-X80 pipeline steel was studied in both acidic and alkaline solutions.
► The correlation between the microstructure and corrosion behaviour of the samples was investigated.
► Presence of M–A phase in the microstructure enhanced the passivity of all samples in alkaline solutions.