PITTING CORROSION BEHAVIOUR OF ST 37 STRUCTURAL STEEL IN SEVERAL CORROSIVE ENVIRONMENTS

Abstract

St37 is constructional steel having maximum 0.17 % carbon ratio, and its fracture strength is between 360-510 MPa. It is used to increase the mechanical properties as rebar material in composite concrete systems. Pitting corrosion is one of the most dangerous detrimental mechanisms for the reinforcing rebar because it is widespread, difficult to control and it has degrading effects in the material. For these reasons, the pitting corrosion behavior of St37 is investigated with respect to the salinity rate of the Black Sea and the Mediterranean Sea to observe the influence of salt to the reinforcing rebars of buildings used in these regions. Several standards such as EN, ASTM or ISO could be used for the pitting corrosion experiments but the authors have decided to develop their own procedure to become as standard protocol for this research. Cutting from plate, St37 dogbone specimens are prepared two for pristine, two for 3.5 % NaCl solution and two for 1.8 % NaCl solution and they are sanded with sandpapers to obtain clean surfaces. To observe corrosion distinctly and giving ID numbers to the pits, the corrosion exposed area is adjusted to 1 mm2 and the rest of the specimens are painted with nail polish. 1.8 % and 3.5 % are the salinity rates of the Black Sea and the Mediterranean Sea respectively, two different solutions are prepared and the dogbone specimens are immersed into these solutions based on the determined corrosion protocols. Pre-corroded specimens are then investigated under optical microscope to identify and measure the corrosion pits and these specimens are put to tensile test to obtain the stress-strain curves of the same specimens. The surfaces of the specimens are characterized by using Scanning Electron Microscope (SEM) to identify where the fracture originated from. The %3.5salinity rate results more pits on the surface, deeper pits from the surface and the 1.8 % salinity rate results less pits on the surface and shallower from the surface. Moreover, it is observed that increase in salinity rate decrease the mechanical properties after tensile testing results.

Keywords

• Construction, Steel, Salinity, Pitting Corrosion

References

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