Corrosion Morphological Characteristics of the Blackening Process on Plate and Cylindrical Workpieces

Abstract

Corrosion is a prevalent issue in metallic materials, leading to significant damage and potential hazards for individuals. Take, for instance, AISI 1015 steel, belonging to the low carbon steel category commonly employed in crafting machine tools. Hence, there is a requirement for a coating solution capable of application without adding thickness to the surface of the workpiece while effectively mitigating corrosion. One effective method for mitigating corrosion is through the application of a blackening coating. The objective of this study is to investigate how varying heating time and temperature during the blackening process of AISI 1015 steel impacts both thickness and corrosion rate. The experimental approach involves subjecting test specimens of AISI 1015 steel, in both plate and cylinder forms, to a salt solution comprising 30% Sodium Hydroxide (NaOH), 10% Sodium Nitrate (NaNO3), 10% Sodium Nitrite (NaNO2), and 50% water (H2O). The specimens will be exposed to different heating durations of 30, 60, and 90 minutes at a constant temperature of 100°C. Next, the blackened material will undergo immersion in hydrochloric acid (HCl) solutions with concentrations of 5% and 10%. The evaluation will involve assessing weight loss for each material and utilizing scanning electron microscopy (SEM) for further analysis. The research show that the thickest surface layer was observed after a 90-minute coating duration, measuring 20.27μm for plate specimens and 19.24μm for cylindrical ones. Regarding corrosion rates, for cylindrical AISI 1015 steel, the lowest rate was recorded at 2662.90 mm/year with a 5% HCL solution, and the highest at 3099.79 mm/year. For plate-shaped AISI 1015 steel, the lowest corrosion rate was 520.68 mm/year with a 5% HCL solution and the highest was 2082.72 mm/year with a 10% HCL solution. It can be concluded that the blackening process results in a thicker and more uniform surface layer on plate-shaped materials compared to cylindrical ones. Consequently, this leads to a lower corrosion rate on plate-shaped materials compared to cylindrical ones.