Cast Iron is a fantastic material that has been used for years and is known for its excellent strength and durability.
We get asked often why cast iron is stronger than pure iron, and the answer is quite scientific and lies in its composition and properties. Below we will go through the characteristics of cast iron and explain why it is harder than pure iron.
What Sets Cast Iron Apart from Pure Iron?
To understand why cast iron is so tough, you need to understand the elements. In an alloy (a metal made of two or more elements) there are atoms of varying sizes. The presence of either smaller or larger atoms distorts the layers of atoms within the pure metal. This means a greater amount of force becomes necessary for these layers to move past each other. As a result, the alloy demonstrates increased hardness and strength compared to the pure iron.
Cast iron is a mixture of iron, carbon, and silicon, with trace amounts of other elements like manganese, sulphur, and phosphorus. The addition of carbon, typically in the form of graphite flakes, is what gives cast iron its strength but also its brittleness. Pure iron, on the other hand, contains almost no carbon, making it softer and therefore less robust.
Cast iron has a microstructure consisting of graphite flakes within the iron. This microstructure creates areas of weakness and strength, making it both tough and brittle at the same time. Pure iron, with its uniform and softer structure, lacks the same level of toughness, but it does mean that is it more flexible unless the cast iron is heated under controlled conditions.
Types of Cast Iron
Cast iron comes in various types, each with unique properties. Some of the common types include:
- Grey Cast Iron: Known for its excellent castability and dampening properties.
- White Cast Iron: Extremely hard and wear-resistant.
- Ductile Cast Iron: Provides a combination of strength and ductility.
- Malleable Cast Iron: Offers good machinability and weldability.
Cast iron has exceptional durability, thanks to its hardness and remarkable resistance to wear. These qualities make it an excellent choice for jobs which require long-lasting and dependable performance. Furthermore, its remarkable heat retention and even distribution make it a perfect material for cooking and heating purposes. Cast iron pans and skillets are the preferred choice for many and will last for years if maintained correctly. Cast iron’s versatility extends to its ease of machining and ability to be cast into intricate forms, making it highly adaptable for a wide range of industries.
Why Cast Iron is Preferred Over Pure Iron
Cast iron consists of only 96% iron, with the remaining 4% consisting mainly of impurities, primarily carbon. These impurities contribute to the brittleness of cast iron.
Once the impurities are removed from cast iron, the atoms in pure iron arrange themselves in a regular pattern. This organised atomic structure assists the easy sliding of atoms over each other, making cast iron highly malleable and flexible. However, pure iron is also excessively pliable for most purposes.
To enhance its properties, most pure iron is transformed into alloys by introducing various additional elements into pure iron.