Corrosion susceptibility behavior in 12Cr–1Mo martensitic stainless steel welded by SAW process and the effect of δ-ferrite in the HAZ

Pitting corrosion in stainless steel (SS) is a punctual defect that promotes fatigue and cracks propagation. Martensitic steel of steam turbine is exposed to the thermal cycle of welding, high pressures, and corrosive environments in the heat-affected zone (HAZ). The presence of δ-ferrite in HAZ causes crystalline grain boundaries sensitization and reduces corrosion resistance. This research evaluated the corrosive effect of NaCl, NaOH, and H2SO4 in critical welding regions (BM, HAZ, FZ) by analyzing potentiodynamic curves, EIS, and mass loss calculation. The δ-ferrite in the HAZ promotes an increase in the corrosion rate in the NaCl and H2SO4 derivatives of the corrosion products formed. Furthermore, the mass loss in the HAZ was more significant than that in the BM and FZ. Despite having a lower Cr content in the FZ. •The presence of δ-ferrite in the HAZ increases the corrosion kinetics in acid environments.•The pitting size does not depend on the corrosion rate.•Passivation zones at stable current density reduce corrosion rate in HAZ.•The low Cr content in the filler metal increases the reaction kinetics in the FZ.