Investigating Corrosion Behavior of Hard Coatings of Iron-base Electrodes Containing Carbide Elements

Abstract

In this research, using the manual shielded metal arc welding (SMAW) process, a wear-resistant layer was created by AMA1600v, AMA1622v, and AMA1623v hard coating electrodes on the St37 carbon mild steel, and the effect of the number of welding passes on the microstructure and corrosion resistance of the coatings was evaluated. For this purpose, optical microscope, scanning electron microscope (SEM) equipped with Energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) were used. The results showed a distribution of different carbide deposits in the microstructure of the coating metals. The deposits were complexs of the carbides of chromium, molybdenum, and vanadium. The results of the XRD demostrated the presence of martensite, austenite, chromium carbide, and molybdenum carbide phases in all three coating metals. Tungsten carbide (W2C) was observed only in the AMA1623v sample. The results of the Tafel polarization test showed that the bare and the 1622v samples had the highest corrosion current density (15.23 µA/cm2 and 7.06 µA/cm2, rspectively) among the under-studied samples, and therefore had the highest corrosion rate and the lowest corrosion resistance. Also, the results of the test showed that the corrosion current density of the 1600v sample (6.29 µA/cm2) was higher than that obtained for the 1623v sample (4.80 µA/cm2), which revealed the lower corrosion resistance of the 1600v sample. In addition, according to the results of the electrochemical impedance spectroscopy (EIS) analysis, the highest charge transfer resistance and coating resistance with the values of 6.3 kOhm.cm2 and 68.5 Ohm.cm2, respectively, belonged to the 1623v sample, which was also proven by the polarization test. Moreover, the lowest charge transfer resistance and coating resistance among the coated samples with the values of 2.73 kOhm.cm2 and 42.5 Ohm.cm2, respectively, belonged to the 1622v sample.