How Does Hot Blackening Work? - Hot blackening is a chemical process that creates a black oxide layer on the surface of ferrous metals (like steel or iron). This layer improves appearance and provides mild corrosion resistance without affecting the part’s dimensions. * Cleaning (Degreasing & Descaling): 1. The part is cleaned thoroughly using alkaline degreasers and acid pickling to remove oil, dirt, rust, and mill scale. 2. Cleanliness is critical to ensure uniform blackening. * Hot Blackening Bath (Black Oxide Formation): - The part is immersed in a hot alkaline salt bath (typically sodium hydroxide with sodium nitrate/nitrite) at around 135–150°C (275–300°F). - A chemical reaction occurs that converts the metal surface into magnetite (Fe₃O₄), a black oxide layer. * Sealing (Usually in Oil): - After rinsing, the part is dipped in a rust-inhibiting oil or wax, which penetrates the porous oxide layer and enhances corrosion resistance. #Hot Blackening Chemical Manufacturer.