The use of stainless steels as concrete reinforcement is becoming increasingly popular in
coastal and marine constructions in order to prevent corrosion induced by chloride ions
penetrating into the concrete. In these highly aggressive situations, the lean duplex
stainless steels have been extensively employed due to their high mechanical and corrosion
resistances. However, the influence of Mo addition on pitting corrosion resistance of
these steels is not clearly understood in alkaline chloride conditions even if this
element is widely associated to an increasing corrosion resistance in acidic and neutral
environments. Therefore, understanding Mo mechanism on corrosion resistance in alkaline
media is hence of major importance to the setting of optimized alloy composition. The
present work aims to study the effect of Mo addition on pitting corrosion properties of
lean duplex stainless steels in alkaline environments (concrete). The results are
discussed with respect to the influence of Mo addition on pitting potential for two
industrial duplex alloys (1.4362 and 1.4462) in several aggressive media mainly in
synthetic, chlorinated and carbonated solution simulating concrete pore environments (pH10
solution with carbonates and chlorides ions). In order to establish the real role of Mo
addition on lean duplex corrosion and passivation properties, the corrosion behaviors of
two specific laboratory lean duplex alloys, which the only difference between then is the
amount of Mo (0 and 3% wt. Mo), are also studied. Furthermore, scanning electronic
microscopy (SEM) was used to verify which phase of duplex microstructure (ferritic or
austenitic) is mostly susceptible to the pit nucleation in these corrosion conditions as
the role of Mo is probably different to each simple phase.