Study of molybdenum effect on pitting corrosion of stainless steel concrete reinforcements

The use of stainless steels (SS) 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. However, the influence of Mo addition on pitting corrosion resistance of these steels is not clearly understood in alkaline chloride conditions even being well stablished the benefictial effect of this element in acidic and neutral environments. Therefore, the understanding of the Mo role on the corrosion resistance of SS in alkaline media is hence of major importance for the setting of optimized alloy composition. The present work aims at studying the effect of Mo addition on pitting corrosion properties of three different stainless steel families (austenitic, ferritic and duplex SS) in alkaline environments (solution simulating a chloride-contaminated-concrete at two alkaline pH values: 10, to simulate carbonated concrete, and 12, to simulate sound concrete). For comparison, an acid (pH=4) and neutral (pH=7) solution were also included in this study and a real cement medium). In order to establish the real role of Mo addition on pitting and passivation properties of the three studied families of SS, the alloy samples were prepared in laboratory under highly controlled conditions. The obtained results were discussed with respect to the influence of Mo addition on pitting potential for industrial alloys (AISI 304, ISI 316, AISI 430, AISI 434, SAF 2304 and SAF 2205) .