Meteoritic iron is the oldest steel type known. Iron was extracted from iron-nickel alloys found in very few meteorites. Therefore, the use of meteoritic iron was very rare and reserved for special occasions, ornaments and ceremonies. As long as 4000 BC, Ancient Egypt has used meteoritic iron for ornaments and spear tips. Even earlier, around 5000 BC, beads made of meteoritic iron were used in Iran, proving that steel has a long standing and diverse history.
Iron replaced bronze because of its superior hardness, which was particularly important in weaponry and tools. While iron can be found aplenty on Earth, it rarely appears as a minimal because its deposit can be primarily found in ore and meteorites. The high melting temperature (Tm(Fe) = 1535 °C) and the low contents of iron in ore were two of the main reasons why iron was not used as much as bronze. Furthermore, in the Bronze Age, iron was more brittle due to high miscellaneous contents.
Historical Steelmaking Processes
In antiquity, steel was produced in bloomeries and crucibles, two types of ancient furnaces made for smelting iron.
Wootz steel is one of the oldest manufactured steels known and has its roots in South India. It is a high carbon steel that is known for its toughness and sharpness. In fact, Damascus steel, which is one of the most used steel types for blades to this day, is made with wootz steel.
Around 400 BC, the Chinese already had quench-hardened steel, which steelmaking process demands rapid cooling of the material that results in a hard surface layer. Two hundred years later (200 BC), the Chinese melted wrought iron along with cast iron to obtain a carbon-intermediate steel.
Since the 19th century, steelmaking has made significant changes, making steel even more economical and attainable for multi-purposes. Furthermore, these evolutions enabled more varieties of steel types and alloy steels.
The ever-growing expansion of the railroads in the 19th century demanded exponential amounts of iron and steel. The invention of the Bessemer Process by Henry Bessemer proved to be extremely useful to mass-produce steel at low costs. The raw material for the Bessemer Process is pig iron, which has a very high carbon content of up to 4.5% as well as other elements such as manganese. In the process, impurities are blown through the molten iron by oxidation. They escape from the material as gas or form a solid after-product. While these ‘impure’ elements can serve as strengthening alloys, an abundance of them can cause brittleness, rust and other negative effects. The result of the Bessemer process is mild steel, a type of steel that has a low carbon content (approximately 0.05–0.25%), making it malleable and ductile. However, mild steel has a lower tensile strength than higher carbon steel.
Since the Bessemer Process, steelmaking has come a long way. But the possibilities of improving and varying steel types have maybe come an even longer way. There are multiple methods to harden steel and plenty of elements to do so. For example, BorTec’s Borocoat® makes use of boron to improve mechanical properties such as wear resistance, hardness and corrosion resistance.
HOW CAN THE PROPERTIES OF STEEL BE CHANGED?
Heat treatments can be used to improve the hardness properties of steel. However, most processes have a negative effect on the CORROSION RESISTANCE of the material. The BORINOX® STAINLESS STEEL HARDENING PROCESS allows you to improve the hardness of stainless steel and NICKEL BASE ALLOYS without compromising corrosion resistance. In addition, the NICKELCOAT® process gives you the opportunity to improve the wear and corrosion protection of your materials. The process applies a nickel-based coating to the surface, and also increases resistance to acid. For professional advice, you can contact our materials specialists today.