Corrosion resistance evaluation of boron-carbon coating on ASTM A-36 steel

Abstract

The ASTM A-36 steel is the main alloy, used in the metal-mechanical industry. In the present study, the effect of boron-carbon coating on the hardness and corrosion resistance of the steel ASTM A-36 was reported. Boronizing thermochemical treatment was carried out at 950 °C for 4 h followed by the carburizing process at 930 °C for 6 h. The corrosion study was conducted using the polarization technique (Tafel) and electrochemical impedance spectroscopy (EIS), which employed a fused deposition modeling-based 3D printing electrochemical cell made of polylactic acid (PLA). A commercial platinum foil and an Ag/AgCl (3.5 M KCl) electrode were used as the counter and reference electrode, respectively. The working electrode used an area of 1 cm² of the sample. Optical microscopic analysis shown that borides formed on the surface of steels has a saw-tooth morphology and a uniform coating with a thickness of about 60 µm in both samples. The carburizing over boride promoted the formation of coatings on the outermost layer of the samples with a thickness of about 17 µm over the boride layer. Boride formation was verified by X-ray diffraction (XRD) analysis indicating only the formation of the Fe₂B phase. Results showed that boride samples exhibited inferior corrosion resistance compared to original samples, but after carburizing, an outer layer was formed, with the hardness and corrosion resistance like that of the original sample.