The modern era of steelmaking traditionally began in 1855 with the introduction of the Bessemer process which consisted in blowing air through the molten iron to speed the process of oxidation and removal of various impurities from the metal. This allowed a production of large quantities of quality steel at an affordable rate. Steelmaking was further improved in the 20 th century by the Linz–Donawitz-steelmaking method, better known as basic oxygen steelmaking (BOS), which today accounts to roughly 60% of all global steel output. Most of the other 40% is produced by the Electric Arc Furnace (EAF) method that heats charged material by means of an electric arc. Although both methods use large quantities of recycled scrap metal, the EAF method is particularly useful in its capacity to produce steel from 100% recycled scrap metal, while the BOS method always requires a certain minimum amount of metal ore content to start with.

This makes modern steel one of the highest recycled materials on the planet. Today recycled steel accounts for over 85% of used material in global steel production. This has reduced both the need for large scale iron mining operations and the need for some countries to import iron ore at a high cost, bringing key economic and environmental benefits.

Although the steel now has the required shape, hardness, and consistency, it still requires protection from rusting. At this point, an additional step is required which is particularly pertinent to metal roofing, namely galvanization – the application of a protective zinc coating to the metal. The most common and effective method of galvanization is what’s known as hot-dip galvanization. In this process the steel strips are cleaned from any oils and dirt with a caustic solution. The solution is then rinsed off and the steel is pickled in an acidic solution to remove mill scale on its surface (iron oxide) and rinsed again. A flux of zinc ammonium chloride is then applied in order to inhibit oxidation. The steel is then dipped into a molten zinc bath and held there until its temperature equilibrates with the temperature of the molten zinc.

After the temperature settles, steel is removed from the bath, the zinc layer is blown off by air wipers until the desired coat thickness is reached, and the metal is cooled in a quench tank. Among other layers, the most important is an application of a chromate layer to prevent ‘white rust’ (caused by the oxidation of the zinc coating). The final step is to inspect the steel strip, oil it, cut it at desired length, and to coil it.