Galvanneal is a carbon steel product coated in a mixture of iron and zinc. This steel product is most famously used in the manufacture of cars, although it has a wide range of other uses as well, including in construction of structures and ships. Steel mills produce galvanneal by request for customers, and some manufacturing facilities may make their own galvanneal to control every step of the process.
The term “galvanneal” is a portmanteau of “galvanized” and “anneal.” Annealing is a process in which metal is subjected to a heat treatment to force it to develop specific desired properties. Galvanization is a process in which metal is coated in a material which will help it resist corrosion. Zinc is classically used for galvanization. The blend of these two processes is designed to give galvannealed steel some unique and very desirable properties which make it ideally suited to an array of applications.
In galvanneal, the steel is first dipped in a hot bath of zinc, as is done when materials are galvanized. Then, it is subjected to a secondary process in which iron is annealed with the zinc coating to create an iron-zinc blend on the surface of the metal. The galvanneal coating is a dull gray in color, unlike the distinctive spangled coating seen on metals galvanized with just zinc. The coating should also stay firmly adhered to the metal for its lifetime, thanks to the heat treatment process.
Galvanneal comes in a variety of thicknesses, including custom sizes which can be created by request at a steel mill. The dull gray surface of galvanneal is very easy to paint, making it appealing for applications in which the metal will be painted, such as car manufacturing. The metal will also resist corrosion. Over time, however, corrosion can develop. Damage to the surface of the coating can expose the underlying steel, allowing rust to set in. Some causes of damage include highly corrosive chemicals, gouges, and collisions.
Galvannealing is a complicated process with a number of steps and a series of areas in which the process can go wrong, rendering the steel useless. Special equipment is required to complete the process, as well. As a result, galvannealed steel is more expensive than steel which has not been processed in this way. This product is used when high performance, safety, and reliability are desired. Cars, for example, must adhere to a number of safety standards and galvannealed steel assists with safety goals for car manufacturers.