True to its name, blue steel is bluish black in color and easily distinguishable from the dull grey appearance of galvanized steel. Although it may appear to merely be an external difference, it is this variation in color which is reflective of the two different procedures undergone by the original steel to acquire protection against corrosion. While the appearance of blue steel is attributed to the coating of the black oxide of iron, galvanized steel owes its distinct grey color to zinc carbonate, a result of the chemical reaction between zinc, oxygen and carbon dioxide. The intention behind the creation of both varieties, however, is to wage a successful war against rust, the most destructive corrosive agent.
Bluing steel is achieved through the process of passivation, which neutralizes the non-reactive film of oxide on its surface. In comparison, galvanizing steel is formed by dipping the steel in molten zinc and immediately exposing it to the atmosphere to facilitate the solidification of the protective coating. As finished products, blue steel takes on a bluish hue, and galvanized steel can be easily spotted courtesy of its spangled appearance, which is caused by the crystallized patterns on the surface. Blue steel can also be created using different processes such as hot bluing, cold bluing, rust bluing and fume bluing, but galvanization has been a standard procedure, with the only innovation being electrogalvanization, which involves electrifying the zinc to create the protective coating.
Traditionally, blue steel has been associated with the gun industry; for example, firearms manufactured from this material are more resistant to rust and tend to last much longer. The ingenious engineers of this era have also found various other applications for this type of steel, and now its use is widespread in setting up massive steel structures for numerous industries. Galvanized steel, on the other hand, has been the backbone of the steel industry, and boasts use on commercial, structural formations and drawing applications, due to its easy malleability and ductility. It is only in recent years that blue steel has been substituted for galvanized steel in structural engineering.
Another noteworthy point pertaining to blue steel is that the process of bluing is effective solely in the case of steel and stainless steel. Galvanization encompasses both iron and aluminum, both of which are often more readily available. The bluing application process on non-ferrous materials, such as aluminum and polymer, has proved to be completely ineffective, as the protection granted after the bluing process has been found to be virtually non existent.