Stainless steels: Passive film composition, pitting potentials, and critical chloride content in concrete

Stainless steel reinforcing bars show excellent corrosion resistance in concrete structures exposed to harsh environments. Only a little information on the surface chemistry of these materials in alkaline media is available. This study reports the X-ray photoelectron spectroscopy surface analytical results (thickness, composition of the passive film and of the interface beneath the film) obtained on black steel, FeCr alloys, DIN 1.4301, DIN 1.4462 and the nickel-free DIN 1.4456 after exposure to alkaline solutions simulating concrete. The pitting potentials of the steels could be related to the Cr(III)oxy-hydroxide and Mo(VI) content in the passive film. C-crit, the critical chloride content for corrosion initiation in concrete, necessary for life-time predictions, can be determined only with time-consuming tests, especially for high-alloyed stainless steel. This study reports a correlation between C-crit in concrete (made with CEM II-A/LL and CEM I) and the pitting potential for carbon steel, Fe12%Cr alloy, DIN 1.4301, and DIN 1.4571 stainless steels. This could allow, for the first time, a quantitative estimation of C-crit for stainless steel in concrete based on short-term solution tests.