Iron the Underdog
June 2019
Iron is one of the most important stepping stones towards steel production. Demand for iron ore can be almost entirely predicted by demand for steel, and as such steelmakers are the largest consumers of iron in all its forms.

But “almost entirely” is not 100%. A small percentage of iron and iron ore does go towards uses other than steel, with five key iron alloys comprising most of iron ore’s non-steel end-use scenarios:

  • White Iron
  • Gray Iron
  • Ductile Iron
  • Malleable Iron
  • Wrought iron

These alloys generally contain 2-4% carbon—significantly higher rates than steel, which typically contains between 0.05% to 1.5%. Wrought iron, which makes up a separate set of end-use cases to most cast iron or steel, contains between 0.05% to 0.1% carbon, and around 1-2% slag.  


Wrought Iron

While its tensile strength and resistance to corrosion has historically allowed wrought iron usage in horizontal beams and weather-exposed construction, it has been entirely replaced by steel in most, if not all, practical use cases. Wrought iron is generally now used for outdoor decorations, some magnetic uses, and sees some limited deployment in fences, window grilles, shelving, and security doors.

Wrought iron is generally the purest form of iron found in manufacturing, but this purity is its weakness. Mixing with other metals and carbon to create alloys and steels is what, historically, has made iron such a useful and versatile material.


Cast Iron (Gray & White)

Compared to wrought iron, cast iron sees a relatively wide range of uses with many of them being quite practical and not at all decorative—although, due to its relative cheapness, cast iron is used in a number of indoor decorations, despite being somewhat limited by its brittle quality.

Unlike wrought iron, which can be heated and worked into shapes, cast iron must generally be melted and cast into a mould—hence the name.  Each of the four kinds of cast iron has a slightly different set of properties, appearances, and end uses.

Gray cast iron, being the cheapest and most widespread form of cast iron, is likely the form that most people are familiar with. Characterised by a darker colour, good machinability (with a tendency to powderise rather than chip), high thermal conductivity, and strong resistance to wear and friction, this form sees usage in cast iron pots and pans, disc brake rotors, and a variety of mechanical parts that dampen vibrations—such as suspension components and housings.

White iron, the second-most common cast iron, is produced by a rapid cooling of iron during casting. It is a high-carbon iron with high compressive strength and strong wear resistance that retains its shape and hardness even while heated. While limited in use by its brittleness, the wear-resistant material is used as liners in industrial machines—such as cement mixers, ball mills, or extrusion nozzles—or in components where its hardness and toughness is an asset, such as drawing dies and grinding mills.


Malleable Iron and Ductile Iron

The remaining two cast irons, malleable iron and ductile iron, are respectively more malleable and ductile than other cast irons.  If you’ve been paying attention, this won’t surprise you: the hint about each alloy’s properties is cunningly hidden right there in the name.

Malleable iron is often used in the construction of small parts, largely due to its high tensile strength. It sees usage in electrical fittings, hand tools, pipe fittings, and other small-scale parts. Ductile iron is used in many of the same areas, particularly in pipes, valves, and other liquid-management uses, but maintains a reliable advantage over malleable iron due to its superior casting and machining qualities, higher overall strength and ductility, and slightly cheaper manufacturing cost.



Iron Ore Tailings

 Moving away from direct iron products, iron ore tailings do have some limited and not terribly exciting forms of reuse. Largely, tailings hold potential for reuse in the manufacture of cement, concrete, and ceramics. When making clinkers and cement, iron ore tailings can substitute for conventional aggregates, improving compressive strength and keeping consistent mechanical and tensile strength. Iron residue can also be used in the making of red ceramics, colouring the material and adding mechanical sturdiness.

Overall, though, the vast majority of iron ends up in some form of steel. It is the metal which much of our world is built upon, and will likely remain so for the foreseeable future.