A phosphate coating is a coating application used to add anti-galling and rust inhibiting characteristics. Phosphate coating is the treatment of castings, iron, steel or steel-based substrates with a solution, whereby the surface of the metal is converted to an integral, mildly protective layer of insoluble crystalline. Phosphating is considered the heart of pretreatment operations; it is here that the top surface of the metal is converted into a highly insoluble, corrosion-resistant coating that provides the primary bond between substrates and the next process.