Cast iron can refer to a range of iron alloys, but it is most commonly associated with gray iron. Despite having the name iron, it isn’t pure elemental iron (Fe on the periodic table)—it’s actually an alloy containing 2–4 percent carbon, plus small amounts of silicon and manganese. Other impurities, such as sulfur and phosphorus, are also common.
Cast iron is formed by smelting iron ore, or melting pig iron (an intermediate product of iron ore extraction), and mixing it with scrap metals and other alloys. The liquid mixture is then poured into molds and allowed to cool and solidify.
The final result is strong but brittle. Due to the higher carbon content, cast iron solidifies as a heterogeneous alloy, meaning it contains multiple constituents, or materials in different phases, within its microstructure.
Cast iron is very brittle in nature, meaning it’s comparatively hard and non-malleable
This mixed microstructure is what gives cast iron its distinctive physical properties. The internal carbon particles create internal stress points conducive to fracture. Cast iron is harder, more brittle, and less malleable than wrought iron. It cannot be bent, stretched, or hammered into shape, since its weak tensile strength means that it will fracture before it bends or distorts. It does, however, feature good compression strength.
Cast iron is a group of iron-carbon alloys with a carbon content greater than 2%. It is made by re-melting pig iron along with substantial quantities of scrap iron, scrap steel, limestone, carbon (coke). Care is taken to remove the unwanted contaminants from the process as this could affect the quality of the cast iron produced.
Cast iron is used in a variety of applications including cookware, bridges, textile mills, buildings and others. It is also used in metrology and precision work due to its specific characteristics.
Casting is significantly less labor-intensive than manufacturing wrought iron, and was a prominent form of production throughout the 18th and 19th centuries. The advent of steel and automated machining technologies have reduced the role of casting in some industries, but it remains a cost-effective and widely-used process in many others. While steel has almost entirely displaced cast iron in construction, cast iron remains popular for products with complex shapes that are easier to cast than machine to shape. Cast iron is less reactive with mold materials than steel, and has a lower melting point, making it more fluid.
Cast iron and wrought iron are both susceptible to corrosion when bare surfaces are exposed to oxygen in the presence of moisture. This can be challenging for outdoor environments with near-constant exposure to precipitation and humidity. Unlike other metals that form a protective oxidative coating, iron will, given enough time, rust and flake away entirely.
To prevent rust, iron products should be coated to prevent exposure. Paint is commonly used to coat and protect bare metal. Powder coating is another method, ideal for outdoor furnishings more susceptible to wear in high-traffic areas. Powder coatings are highly durable and won’t fade, chip or crack over extended periods of time.
From Lincoln, Massachusetts to Lincoln, Nebraska to Lincoln, Ontario, North America is rich with history. Every town has a story to tell, and the buildings in these towns have played as much a part in crafting the past as the people themselves.
When restoring historical buildings with architectural iron and metalwork, quality and authenticity are critical. Large outdoor elements such as bollards, gates, fences, lamp standards, and park benches play a significant role in setting an ambiance faithful to historical times. Modern foundries can reproduce early metalwork by taking their design cues from historical drawings or the original structures themselves.
Before you get yourself a cast iron tool or product, check out the following pros and cons of this material:
Cast Iron Pros