A new duplex stainless steel, $32101, was chosen in this work for investigation of the corrosion properties in an environment corresponding to concrete pore solutions. The new duplex stainless steel was developed for general use and with high mechanical strength. Furthermore, the steel has a chemical composition corresponding to a corrosion resistance similar to that of type 304 or better. To balance the ferritic-austenitic microstructure nitrogen and manganese are used instead of expensive nickel. In this work a general screening of the corrosion resistance of this steel grade is presented. First, this includes results from a test program regarding uniform corrosion, where a number of steel grades in addition to the new duplex steel grade were tested according to a test program specified by the Materials Technology Institute, MTI and standardized as ASTM G 157. Then, results from laboratory corrosion tests regarding pitting corrosion, intergranular corrosion and stress corrosion cracking were compared for the new duplex steel to the standard austenitic stainless steels. Finally, the suitability of using this new duplex steel as reinforcements in concrete was investigated. For this purpose, rebars of UNS $32101 were compared with standard stainless steels, using electrochemical tests to screen the corrosion resistance. The test solutions were artificial solutions corresponding in alkalinity and chloride contents to concrete pore solutions. High corrosion resistance was obtained for the new duplex stainless steel in these solutions. These results were also discussed and compared with a field test carried out in a concrete bridges- survey. .
Stainless Steels as reinforcement is a new application for stainless steels. Some examples of stainless steel grades used as reinforcements in concrete are of type 304, 304N, 316LN austenitic steel grades and UNS $32205, a duplex stainless steel grade with higher strength. The objectives, at present time, for altemative materials in reinforcements are improvement of properties and cost reduction. In this study the corrosion properties of a new duplex stainless steel grade LDX2101 ®(1), UNS $32101 (EN 1.4162) is presented. 10utokumpu Stainless Trade Name The cost saving potentials of using stainless steel $32101 as, for example, reinforcements in concrete, where high strength can be utilized and good corrosion performance is emphasized can be illustrated by good corrosion resistance and in less effort in maintenance.
Localized corrosion such as pitting or crevice corrosion is rather expected in an environment containing chlorides, but commonly the high pH (>12) in concrete is beneficially increasing the corrosion resistance of stainless steels. For uniform corrosion to occur the environment has to be very acidic. However uniform corrosion might also occur in an alkaline environment in combination with a high temperature (100°C/212°F). However, in due time aging of concrete will introduce carbonation when SO3 and CO2 from rainwater penetrate the concrete and the pH is lowered close to 101. Nevertheless, in a concrete pore solution at this high pH the stainless steel would remain in the passive state. Chlorides are also present due to several possible causes such as deicing salts, chlorides in the mixing water for the concrete or any marine environmental influence. The chloride can either be bound into the concrete but also remain as free chlorides in the pore-solution. Calculating the risk for corrosion the amount of free chlorides in the pore-solutions has to be taken into account. Wang and Newman, recently investigated the possibility for crevice corrosion to occur on a steel grade of type 316L in concrete pore solutions at various
