Rust forms when iron molecules in exposed metal alloy surfaces react with oxygen in the presence of water. Rust may also form in the presence of salt, acids, or harsh industrial chemicals.
All steel alloys corrode; however, corrosion-resistant steel is usually made corrosion-resistant for a specific application whereas stainless steel’s superior corrosion resistance will depend greatly on the grade of stainless steel used.
While they can share similarities they are not the same. However, both corrosion-resistant steel and stainless steel are useful for a large variety of products and applications. Choosing the right corrosion-resistant steel alloy for your application would depend on factors such as the environment, cost, formability, heat resistance, strength, and workability.
Stainless steel is most often chosen for its reliable corrosion-resistant properties, but it’s important to be aware that different grades of stainless steel provide different amounts of corrosion resistance.
Austenitic stainless steels like the general-purpose grade 304 provide good corrosion resistance as they contain a high percentage of chromium which oxidizes quickly to form a protective layer of chromium oxide on the surface of the metal. It is this oxide layer that resists corrosion while at the same time preventing oxygen from reaching the underlying steel.
Other elements added to stainless steel such as molybdenum in grade 316 further increase the corrosion resistance. The addition of nickel to grades of stainless steel is another chemical component that adds to the alloy’s rust-resistance properties.
In some cases, like for certain aircraft parts, stainless steel will be primed and top-coated to further increase its corrosion resistance.
Galvanized steel, a type of carbon steel coated with a thin layer of zinc, will eventually rust, but it takes a long time. The protective zinc oxide coating acts as a barrier to prevent oxygen and water from reaching the steel. Even when the zinc coating is scratched off, it will continue to protect nearby areas of the underlying steel through cathodic protection.
Beyond galvanizing, more can be done to carbon steel to make it corrosion-resistant like electroplating, painting, lacquering, oiling and bluing.
Steelmor is the leading supplier and manufacturer of stainless steel in South Africa. Give us a call today on 011 747 5700 for more insight on corrosion-resistant steel and which stainless steel grades will best suit your project.