Hot-dip galvanized (HDGI) steel is often just called galvanized steel, although the full name is more correct. HDGI steel products are prepared by plunging a steel product into a vat of molten zinc. A thin coat of zinc adheres to the steel part and is quickly oxidized by the surrounding atmosphere. Zinc has a much lower oxidation-reduction potential than iron, meaning it reacts with the oxygen in the air much more readily, so it protects the steel beneath and greatly extends its lifespan.

Rolling is a process that shapes the steel to make it more suitable for its intended use. As its name implies, cold-rolling takes place at a temperature where the steel has already recrystallized, although it may still be quite warm relative to room temperature. In this process, steel passes between sets of rollers that squeeze it slightly to alter its shape. Depending on the type of rollers you choose and how they are arranged, you can produce shapes like cylinders, I-beams and sheets.

Cold-rolling and galvanization are not mutually exclusive, and in fact cold-rolled steel can be galvanized. That’s because cold-rolling is a technique for forming the steel, whereas HDG is a technique for treating it to protect it from corrosion. Galvanized steel generally has much better corrosion resistance, although it’s less suitable for high-temperature conditions. Although it can be damaged or scratched quite readily, the zinc layer will continue to provide corrosion protection despite damage to its surface.

In summary, the primary difference is that galvanized steel has a zinc coating for enhanced corrosion resistance, while cold rolled steel undergoes a mechanical processing to improve its physical properties without any additional coatings.