Investigation of corrosion properties of box boring din 20MnCr5 steel bars

Abstract

In this study, boriding process was carried out on Ø11 mm diameter DIN 20MnCr5 quality steel bars, used in chain elements such as links and rings, and fasteners such as bolts, at 950oC boronizing temperature, boriding times of 2.5 and 7.5 hours. In this study, the formation and growth of the boride layer and the metallographic structure, the coating thickness and corrosion properties of the boronized steels were investigated depending on the boriding conditions. In the box boriding process, Ekabor-II powder mixture, with its commercial name, was used as boriding powder. According to the optical microstructure results made as a result of box boriding, the coating thickness was 371.5 μm in the Ø11 mm diameter boronized DIN 20MnCr5 steel bar for 7.5 hours boriding times while it was 195.6 ?m in that steel bar for 2.5 hours boriding times. Corrosion experiments were carried out in solutions prepared by adding 3.5% NaCl to distilled water. According to the results of the immersion test, the lowest corrosion rate in mdd was measured as 112 mg/(dm2 × day) in the Ø11 mm diameter, 7.5 hour boronized sample, and the highest corrosion rate in mdd was 1456.75 mg/(dm2 × day) in the untreated Ø11mm diameter sample. In the potentiodynamic polarization test, parallel results were obtained for immersion corrosion. Corrosion rate values (icor) were measured at the highest value of 209 × 10−6 A/cm2 in the untreated Ø11 diameter sample, while the lowest icor value was 0.0039 × 10−6 A/cm2 in the Ø11 mm diameter sample borided for 7.5 hours.