Optimization of hot alkaline blackening process for production of magnetite layer on a steel substrate

Abstract

Magnetite thin film obtained from the hot alkaline nitrate blackening method is been utilized for the protection of the surface of steel. This study aims to investigate the effect of varying some parameters for instance, blackening bath's nitrate concentration, temperature and dwell time on the properties of the magnetite coating, especially that of wears resistance. In order to produce the magnetite coating, mild steel specimens were placed in a boiling solution made up of some compositions of sodium hydroxide and sodium nitrate dissolved in water. The blackened specimens were then undergoing some analysis, which are microstructure analysis using a reflecting microscope. Wear resistance analysis and tribological properties were also done, by using the pin-­‐on-­‐disk test. Consequently it was found that the magnetite coating produced by oxidation process in the blackening experiment, able to improve the wear resistance and corrosion properties of the steel substrate, other than giving the surface a beautiful like mirror finishing. Furthermore in this study, it was found that the best condition to produce a good quality of magnetite coating on steel substrate is by conducting the blackening process in 30% of nitrate bath solution at 140℃ for 15 minutes.