Alloying elements and scrap in stainless steel

The Role of Scrap in a Circular Economy

The sustainability of stainless steel is closely linked to its recyclability. Stainless steel can be repeatedly recycled without losing its essential properties, making scrap a valuable raw material in the production process. The extensive use of recycled stainless steel reduces the demand for virgin raw materials, lowers energy consumption and significantly decreases environmental impacts. Industry studies show that the use of stainless steel scrap generates substantial climate and environmental benefits while supporting a circular economy.

Chromium: The Foundation of Stainless Steel

Chromium is the defining alloying element in stainless steel. It forms a thin, self-repairing passive layer on the surface of the material, which protects the steel from corrosion and oxidation. This unique characteristic is what distinguishes stainless steel from ordinary carbon steel. All stainless steels include at least 10.5% chromium. Many grades contain even more chromium to improve their resistance to corrosion and oxidation at high temperatures.

Chromium is introduced into irons, steels and many superalloys by alloying with the intermediate product, ferrochromium. This is produced by the pyrometallurgical reduction of chromite ore with carbon and/or silicon in high temperature electric arc furnaces.

Ferrochromium is essentially an alloy of iron and chromium which may intentionally contain substantial levels of carbon and silicon.

Nickel: Enhancing Corrosion Resistance and Formability

Nickel is a naturally-occurring metallic element with a silvery-white, shiny appearance. It is the fifth-most common element on earth and occurs extensively in the earth’s crust and core. Nickel, along with iron, is also a common element in meteorites and can even be found in small quantities in plants, animals and seawater.

Nickel improves corrosion resistance, toughness and ductility. It is particularly important in austenitic stainless steels, where it contributes to excellent formability and performance at both low and high temperatures. Nickel-containing grades are widely used in architecture, transportation, food processing and chemical industries.

Molybdenum: Improving Performance in Harsh Environments

Molybdenum is a metallic element which is most frequently used as an alloying addition in alloy and stainless steels.

Molybdenum significantly increases corrosion resistance, especially against chlorides and aggressive chemicals. It also enhances strength, weldability, toughness and high-temperature performance. For this reason, molybdenum-bearing stainless steels are commonly used in marine environments, chemical processing plants and desalination facilities.

Manganese: Strength and Ductility

Manganese is a chemical element with the symbol Mn and atomic number 25. Manganese makes up about 0.1% of the earth’s crust. It is the 4th most used metal on earth in terms of tonnage.

Manganese contributes to the strength and ductility of stainless steels and can partially replace nickel in certain grades. Its addition enables the development of cost-effective stainless steel grades while maintaining good mechanical properties.

Titanium: Protecting Welded Structures

Titanium is used to stabilise certain stainless steel grades during welding. It prevents the formation of chromium carbides in heat-affected zones, reducing the risk of intergranular corrosion after welding. This makes titanium particularly valuable in welded equipment used in demanding industrial applications.

Sulphur: Enhancing Machinability

Although used in relatively small amounts, sulphur plays an important role in free-machining stainless steels. By forming manganese sulphide inclusions, it enables higher cutting speeds and improved machining efficiency during turning, drilling and milling operations.

Cobalt: Additional Strength and Corrosion Resistance

Cobalt can improve the strength of stainless steels and contribute to the stability of the passive layer. This helps further enhance corrosion resistance in specialised grades designed for demanding applications.

Vanadium: Wear Resistance and Hardness

Vanadium increases strength, hardness and wear resistance. It is particularly beneficial in stainless steels used for knives, cutting tools and other applications where edge retention and durability are essential.

Tungsten: High-Temperature Performance

Tungsten enhances strength, toughness and corrosion resistance at elevated temperatures. Stainless steels containing tungsten are therefore well suited for applications involving high levels of heat and thermal stress.